# Cyclopedia of Painting/Useful Information

USEFUL INFORMATION.
Alabaster, To Clean. Make a paste with quick-lime and water, spread this well over the discolored article, and leave it on for about twenty-four hours, then remove with soap and water, applying some friction on parts which are worse than others. Alabaster, if not too much discolored, may be cleansed with a strong lye of soap and water, or, the superficial dirt and grease having been removed, it may be washed with diluted muriatic acid.
Glass, To Remove Grease From. Dissolve carbonate of soda in water, in the proportion of 1 of the former to 10 of the latter, and let the liquid boil in a clean untinned iron pot. Slake 8 parts of quick-lime in a covered vessel, and add the hydrate thus formed to the boiling liquid, stirring it meanwhile. Great care must be exercised in using this caustic solution, which must not be allowed to touch the hands, the glass must therefore be dipped in it by the aid of tongs or pliers. When the grease is dissolved the glass is to be well brushed and subsequently rinsed in water.
Gold Size. Heat $^1$⁄$_2$ pound linseed oil in a flask, and gradually add 2 ounces of powdered gum animi, stirring the oil continuously until the whole of the gum is dissolved. Continue boiling until the mixture becomes a little thicker than tar, when it must be strained through a coarse cloth. Previous to use, it is to be ground up with sufficient vermilion to render it opaque, and turpentine must be added in order that it may work freely.
The following method of making gold size is derived from a very old source, and is given in the words of the original:
​To Make Gold Size. Take Gum Animi, Asphaltum, of each 1 ounce, minium litharge of gold and umber, of each $^1$⁄$_2$ ounce, reduce all into a very 'fine powder, and add to them, of linseed oil 4 ounces, of drying oil 8 ounces, digest over a gentle fire that does not flame, so that it may only simmer and bubble up, but not boil, for fear it should run over and set the house on fire. Keep constantly stirring with a stick till all the ingredients are dissolved and incorporated, and do not leave off stirring it till it becomes thick and ropy, and is boiled enough, let it stand till it is almost cold, and then strain it through a coarse linen cloth, and keep it for use. To prepare for use, mix with oil of turpentine during heating, and strain again, add vermilion, and thin as required with turpentine.
Iron-work, Paints for preserving. Plumbago and hot coal tar.
Equal parts of asphaltum and rosin dissolved in common turpentine.
For machinery, dissolve 2 pounds india-rubber, 4 pounds resin, 2 pounds shellac in 5 gallons of benzine. This may be used with any other paint as a vehicle.
Wrought-iron bridges, are painted with white lead as follows: The iron-work is first made clean by scrubbing and brushing it with wire brushes, this done, all the cavities and fissures are filled up with a putty of litharge, linseed oil, varnish, and white lead. This filling being dry, brushing is repeated. Afterwards paint is applied consisting of 300 pounds of white lead, 10 gallons of crude linseed oil, and 1+$^1$⁄$_4$ gallons of turpentine. This paint is repeated when the previous coat is sufficiently dry, and finally evenly overspread with white sand. Galvanizing is also employed to prevent rusting. A galvanizing paint consists chiefly of zinc powder and oil varnish. Rusting is further prevented by rubbing the red hot iron with wax, tallow, pitch, or coal tar. Rubbing with heavy petroleum is also well adapted for keeping iron-work clean.
​Marble, Jasper, Porphyry. To clean. Mix quick-lime with very strong soap-lees until the liquid is about the consistence of milk, paint it over the substance to be cleaned, and leave it on for twenty-four hours, after which it is to be washed off, and the stone is to be well rubbed with putty-powder and olive oil.
Marble which has not been tarnished by exposure to the open air may be well washed with potash-water, and subsequently with water with which a small quantity of hydrochloric acid has been mixed.
Mix soda, pumice stone, and finely powdered chalk, in proportions of two parts of the former to one each of the latter, pass these ingredients through a fine sieve, and mix them with water so as to form a paste of some consistency. This paste on being well rubbed into the marble will remove the stains, the marble is then to be washed with soap and water, when a beautiful polish will be produced.
Clean with diluted muriatic acid, or soap and warm vinegar. Dissolve 1+$^1$⁄$_2$ pounds of potash in a gallon of water, add 1 pound of virgin wax, and let the whole boil for half an hour, then allow it to cool, when a cake of wax will be formed on the surface. This cake is to be ground up in a marble mortar, soft water being added, until a smooth paste is formed, and this laid on the marble, and well rubbed with a piece of flannel when dry, will produce a good polish.
Paint, Anti-corrosive. Take equal parts by weight of whiting and white lead, and half the quantity of fine sand, gravel, or road-dust, and a sufficient quantity of coloring matter. This mixture is made in water, and can be used as a distemper-color, but it is more durable to dry it in cakes or powder after mixing, and then use it as an oil-paint by grinding it again in linseed oil. The proportion of oil recommended for this purpose is 12 parts by weight of linseed oil, 1 boiled linseed oil, and 3 sulphate of lime, well mixed. One gallon of this prepared oil is used to 7 pounds of the powder.
​Paint, Economical. Skim milk 2 parts, fresh slaked lime 8 ounces, linseed oil 6 ounces, white Burgundy pitch 2 ounces, Spanish white 3 pounds. The lime to be slaked in water exposed to the air, mixed in one-fourth of the milk. The oil in which the pitch is previously dissolved to be added a little at a time, then the rest of the milk, and afterwards the Spanish white. This quantity is sufficient for twenty-seven square yards, two coats.
Paint for Wire-work. Boil good linseed oil with as much litharge as will make it of the consistency to be laid on with the brush, add lamp black at the rate of 1 part to every 10 by weight of the litharge, boil three hours over a gentle fire. The first coat should be thinner than the following ones.
Paint, To remove old. Wet the place with naphtha, repeating as often as is required, but frequently one application will dissolve the paint. As soon as it is softened, rub the surface clean. Chloroform, mixed with a small quantity of spirit ammonia, has been very successfully employed in removing the stains of dry paint from wood, silk, and other substances.
Paint, To destroy. Mix one part by weight of pearlash with three parts quick-stone lime, by slaking the lime in water and then adding the pearlash, making the mixture about the consistency of paint. Lay the above over the whole of the work required to be cleaned with an old brush, let it remain fourteen or sixteen hours, when the paint can be easily scraped off.
Paint, To remove. In those cases where it is requisite to remove painting entirely from its ground, it is usual to resort to mechanical scraping, or to the very dangerous operation of setting fire to the painted surface immediately after washing it over with oil of turpentine, called turps, for burning off the paint from the old disfigured work, an operation which may be safely and more easily accomplished by laying on a thick wash or plaster of fresh-slaked ​quick-lime, mixed with soda, which may be washed off with water the following day, carrying with it the paint, grease, and other foulness, so that, when clean and dry, the painting may be renewed as on fresh work.
Paint, Metallic. Break common resin into dust or small pieces, and dissolve in benzine or turpentine until the solution acquires the consistency of syrup or molasses, or, equal parts of each of the above hydrocarbons, and any other hydrocarbon that will dry and combine with drying oils, can be used instead of turpentine or benzine. "When the solution is complete, it is gradually added to oxide of zinc, which has previously been made into a paste with boiled linseed oil, until the whole mixture acquires the consistency of a paint suitable for-use. A white paint of a durable and glossy character is thus produced. Other pigments, such as sulphate of barytes, oxide of iron, Brunswick green, or red lead, can be added to make any desired color of paint. One great advantage of its use is its effectual resistance to heat and moisture. It never blisters or cracks even under the hottest sun or in the most inclement weather.
Painted work, To clean. When painted wainscot or other wood requires cleaning, soft soap and fuller's earth should be applied with a flannel. The work should proceed from the top downwards, and the water should be prevented from running on the clean parts as much as possible, or marks will be made which will appear after the whole is finished. One person should dry with a soft rag as fast as another has scoured off the dirt and washed off the soap. When the paint is soiled in parts only, and does not require a general cleaning, dip a sponge or a piece of flannel into soda and water, wash it off quickly, and dry immediately, or the soda will eat off the paint. When paint simply requires to have the dust removed from it, a cloth should not be used, but, after blowing off the loose particles with a pair of bellows, the operation should be completed with a ​long-haired brush. With care, paint will look well for a long time if guarded from the influence of the sun.
Painting, Effect of, on Wood. It is, of course, generally understood that the main purpose of painting wood is to preserve it from decay, but this effect is only to be expected when the wood is previously quite dry, if this is not the case, the painting is injurious instead of being beneficial to the timber. There is a cause which affects all wood most materially, which is the application of paint, tar, or pitch before the wood has been thoroughly dried. The nature of these bodies prevents all evaporation, and confines the internal moisture, which is the cause of sudden decay. Both oak and fir posts may be brought into a pre-mature state of decay, by their having been painted prior to a due evaporation of their moisture, and painting affords no protection to timber against dry rot. On the other hand, the doors, pews, and carved work of many old churches have never been painted, and yet are often found to be perfectly sound, after having existed for centuries. Painted floor-cloths are very injurious to wooden floors, and soon produce rottenness in the floors that are covered with them, as the painted cloth prevents the access of atmospheric air, and retains whatever dampness the boards may absorb, and therefore soon causes decay, carpets are not so injurious, but still assist in retarding free evaporation.
Putty, To make. Pulverize the required quantity of whiting, which has been specially dried, and pass through a sieve of about forty-five holes to the square inch, mix the powder with as much raw linseed oil as will form it into a stiff paste, which should be well kneaded and left for a day or so, it must then be worked up, a small quantity at a time, so that it may be rendered quite smooth, and that balls of the dry whiting powder may not be imprisoned in different parts of the putty, for these would make their appearance when the putty was being used, and would of course injure the adhesiveness of the composition. Putty ​should be kept in an earthenware pan covered with a wet cloth. Putty which has become hardened may be made again fit for use by warming and beating it up, and kneading it whilst in that condition. For particular purposes, as for fanlights, iron-framed greenhouses, and other places where the lap or hold is very narrow, a little white lead may with advantage be added. To color putty, mix red ochre, lamp black, or other color with the whiting.
Putty, To soften. Slake some quick stone lime in water, and add one-third of the quantity of pearlash, make the mixture about the thickness of paint. Apply it with a brush to the putty on both sides of the glass, and leave it on for a day or so, the putty will then have become so softened that it may easily be removed with a glazier's knife, and the pane of glass may then be taken out.
Size, To make. Practically, size is merely glue so much diluted with water that it does not for a very long time harden in the mass, but preserves a jellified condition, and is thus sold in barrels. A better kind is however supplied, made into very thin square cakes like glue, which is principally used for sizing wood which has been stained, or for refined purposes. Parchment size is the best for distemper colors, and is made in the following manner: Place a quantity of parchment cuttings in an iron kettle, cover them with water, and allow them to soak thoroughly, from twenty-four to thirty-six hours will be required for this purpose, and should the water have been absorbed, more must be added. The whole is then to be boiled for about six hours, during which the scum which rises must be removed. It is afterwards to be strained through a coarse cloth. Size prepared in the following manner will keep good for several weeks: Dissolve 3 or 4 ounces of alum in boiling water, and add the solution to every pailful, boil and strain the size a second time, and set in a cool place.
Size, Glove-leather. Take $^1$⁄$_2$ pound of the cuttings of white glove-leather, put them into water and allow them ​to steep for about twelve hours, add about 6 quarts of water, and allow the mixture to boil down to 1 quart, strain, and allow to cool.
Smell of Paint, To get rid of. Place a vessel full of lighted charcoal in the middle of the room, and throw on it two or three handfuls of Juniper berries, shut the windows, the chimney, and the door, twenty-four hours afterwards the room may be opened, when it will be found that the sickly and unwholesome smell will have left. The smoke of the Juniper berries possesses this advantage, that should anything be left in the room, such as tapestry, it will not be in any way injured.
Plunge a handful of hay into a pail of water, and let it stand in the newly painted room.
Fill three or four tubs with about eight gallons of water, and an ounce of vitriol, and place them in the newly painted room near the wainscot. The water will absorb the effluvia from the paint in about three days, but it should be renewed each day during that time.
Soft Putty. This is made of whiting and boiled linseed oil, with white lead in the proportion of one-tenth of the whiting, a small quantity of salad oil is then to be added in order to prevent the white lead from hardening and cracking off, as common putty often does in certain situations.
Varnish, Green transparent. Thin some copal varnish with turpentine, grind well together equal quantities of Chinese blue and chromate of potash, and mix them thoroughly with the diluted varnish.
The precise shade of green may be varied by the different proportions in which the Chinese blue and chromate of potash are used.
For Venetian blinds, give the wood a couple of coats of light lead-color, and allow it to become perfectly hard. Grind some dry white lead in spirit of turpentine, and add to it one-third of its quantity of verdigris or navy green, ​which has previously been ground in oil, to this mixture add sufficient common oak varnish to bind the color. Two, or if required, three coats of this varnish are now to be applied, and as it dries very rapidly the whole may be finished in a few hours.
Varnish, To remove, from Pictures or Fine Work. By friction, if it be a soft varnish such as that of mastic, the simple rubbing of the finger ends, with or without water, may be found sufficient, a portion of the resin attaches itself to the fingers, and by continuous rubbing removes the varnish. If it be hard varnish such as that of copal which is to be removed, friction with sea or river sand, the particles of which have a rotundity that prevents their scratching, will accomplish the purpose. The solvents commonly employed for removing varnish are the several alkalies, alcohol and essential oils used simply or combined. Of the alkalies, the volatile in its mildest state, or carbonate of ammonia, is the only one which can be safely used in removing dust, oil, and varnish from a picture, which it does powerfully, it must, therefore, be much diluted with water, according to the power required, and employed with judgment and caution, stopping its action at the proper time by the use of pure water and a sponge. A thick coat of wet fuller's earth may be employed with safety, and, after remaining on the paint a sufficient time to soften the extraneous surface, may be removed by washing. Both pictures and gilding have been restored to their original beauty by the application of wet clay.
Worm in Wood-work, Prevention of. The ravages of worms and insects are among the principal causes of the destruction of timber. Some woods are more subject than others to be destroyed by them, such as alder, beech, birch, and in general all soft woods of which the juices are of a saccharine nature. Against the common worm, oil of spike is said to be an excellent remedy; and oil of juniper, or of turpentine, will prevent them in some degree. A free ​use of linseed oil is a good preservative, and so is a covering of copal varnish, but these can be applied to small articles only. Another application is sulphur which has been immersed in nitric acid and distilled to dryness, which, being exposed to the air, dissolves into an oil, the parts to be secured from the worm are to be anointed with this oil, which does not give an unpleasant odor to the wood. Lime is an excellent prevention against the worm, and sap-wood should always be impregnated with it when used in a dry situation. As worms do not attack bitter woods, soaking wood in an infusion of quassia has been tried, and is said to have the desired effect.
Zinc, To prepare for painting. In 64 parts of water, dissolve 1 part of chloride of copper, 1 of nitrate of copper, and 1 of sal ammoniac, and add 1 part of commercial hydrochloric acid, brush the zinc over with this mixture, which gives it a deep black, leave it to dry for twenty-four hours, when any oil color will firmly adhere to it, and withstand both heat and damp.
A Useful Cement. Alum and plaster of Paris, mixed with water and used in the liquid state, form a hard composition and a useful cement.
Barytes in Chrome Yellow. The detection of baiytes in chrome yellow is a very simple matter, and as it is a very commonly employed adulterant, the following may be found useful: Put a small portion of the yellow into a test tube, add a sufficient quantity of concentrate muriatic acid, and boil. The yellow is almost immediately resolved into a white semi-crystalline chloride of lead and a green solution of chloride of chromium. A large amount of water is added to the test, which is again boiled. If there is no barytes present, a clear solution will be formed, as chloride of lead is soluble in boiling water. The barytes, if present, will be left behind as a heavy, fine white deposit, which may be washed by repeatedly boiling with water.
Bathrooms. These should be warm in coloring, to assist ​a feeling of warmth during the winter toilet, and they should of course be washable in every part, as otherwise the steam from hot baths may destroy the work in a very short time.
Black Varnish for Ironwork. The following is recommended as a good recipe for a black varnish for ironwork: Take $^1$⁄$_2$ pound of asphaltum and $^1$⁄$_4$ pound of resin, and dissolve in 1 pint of turpentine, rub 2 ounces of lamp-black with a little linseed oil to form a paste, and stir this into the first-mentioned ingredients. The mixture, now being ready, can be painted on any ironwork with a soft flat brush.
Boiling Points. Mercury, 630° Fahrenheit, linseed oil, 266° Fahrenheit, olive oil, 412° Fahrenheit, sulphuric acid, 410° Fahrenheit, oil turpentine, 315° Fahrenheit, water, 212° Fahrenheit, and alcohol, 174° Fahrenheit.
Carver's Polish. In 1 pint of spirits of wine dissolve 2 ounces of seedlac and 2 ounces of white resin. The principal use of this polish is for the carved parts of cabinet work, such as standards, pillars, and claws. It should be laid on warm, and if the work can also be warmed at the time it will be still better. All moisture and dampness should be carefully excluded.
Cement for Marble. Stir to a thick batter with silicate of soda, 12 parts Portland cement, 6 parts slaked lime, 6 parts fine lead, 1 part infusorial earth. This is very excellent for marble and alabaster. The cemented objects need not be heated. After twenty-four hours the fracture is firm, and the place can with difficulty be found.
Cement Mortar. About 8 parts of furnace ashes, slag, or coke, 4 parts of slaked lime, and 1 of clay, are taken and mixed dry, so as to form a cement, which, on mixing with water, sets in the ordinary way. The proportions of the materials may be varied so as to produce either an aerial or hydraulic cement.
Cleaning Paint. Provide a plate with some of the best ​whiting to be had, and have ready some clean warm water and a piece of flannel, which dip into the water and squeeze nearly dry, then take as much whiting, as will adhere to it, apply it to the painted surface, when a little rubbing will instantly remove any dirt or grease. After which wash the part well with clean water, rubbing it dry with a soft chamois leather. Paint thus cleaned looks as well as when first laid on, without injury to the most delicate colors. It is far better than using soap, and does not require more than half the time and labor.
Durable Colors. One of the necessary qualifications of (he painter is the knowledge of the colors that will stand the sun and weather. The manufactured chemical colors are generally not very durable, and are therefore not very suitable for outside work. The chrome yellows, chrome greens, and Prussian blues are fugitive, whether used alone or mixed. A combination of two colors of durable nature is often subject to change of tone. Of the more durable colors for external use, the ochres, Indian and Venetian reds, burnt and raw umbers, and burnt and raw siennas may be mentioned. Zinc white, though of less body than white lead, is more delicate and durable, and should always be used in place of white lead at the seashore, where it is especially durable. The action of the salt air injures the lead. The most durable blacks are lamp-black and vegetable black, the most durable yellows are yellow ochre and Naples yellow, both of which have a good body. Chrome yellow is fugitive, and, like other lead salts, it becomes dark in bad air. Of the reds, those to be depended on are the Venetian red, Indian red, light red, and madder lake; carmine lake, vermilion, and chrome red are best avoided on the exterior. The only blue that will stand is ultramarine, though it is expensive. Prussian blue, cobalt. Antwerp blue, and indigo will fade either singly or in combination. The umbers and siennas, burnt and raw, burnt ochres and Vandyke brown, are permanent colors. Raw umber is very ​durable in both water and oil, and does not injure other pigments when mixed with them. The same may be said of yellow ochre, a natural-colored clay, which does not lose its color when mixed with lime, and hence it is well adapted for distemper painting. Mixed greens are not so durable as those direct from copper, arsenic, etc., which are, however, injurious to health. Emerald green made of verdigris and a solution of arsenious acid, and Scheele's green and Vienna green, arsenites of copper, are very poisonous.
Durable Limewash. For one barrel of color wash, $^1$⁄$_2$ a bushel of white lime, 3 pecks of hydraulic cement, 10 pounds umber, 10 pounds ochre, 1 pound Venetian red, and $^1$⁄$_4$ pound lamp-black. Slake the lime, melt the lamp-black with vinegar, mix well together, add the cement, and fill the barrel with water. Let it stand twelve hours before using, and stir frequently while putting it on. This is not white, but of a light stone color, without the unpleasant glare of white. The color may be changed by adding more or less of the colors named, or other colors. This wash covers well, needing only one coat, and is superior to anything excepting oil paint.
Enamelling a Bath. To remove the dirt and grease from a bath, make a strong lye of soda, say 2 pounds of soda to a pail of water, and well scrub it out with this. Then rub it well down with pumice-stone or glass-paper, then wipe out all the dust. To make a good job it will want three coats of enamel. After giving the first coat let it stand for a day, after it is dry, before applying the second, and let it be two days between the second and third coats, to allow it to get thoroughly dry, a very essential point.
Enamelling upon Glass. This is a German method for enamelling glass: A mixture of dry enamel, thick pine oil, and damar lac is laid on the glass in a semi-dried state. After drying the drawing is pressed in. The enamel is then burned. In this way it is possible to reproduce the forms ​of figures in slight relief, the hairs of animals, the feathers of birds, and the veins of leaves.
Filler-up for Nail-Holes. As a material for filling up nail-holes in wood and broken places, the following is recommended as simple and effectual: Take line sawdust and mix into a thick paste with glue, pound it into the hole, and when dry it will make the wood as good as new.
Filling. A very complete tilling for open cracks in floors: may be made by thoroughly soaking newspapers in a paste made of 1 pound of flour, 3 quarts of water, and a tablespoonful of alum, thoroughly boiled and mixed, make the mixture about as thick as putty, a kind of paper putty, and it will harden like papier-maché.
Filling for Cracked Ceilings. Whiting mixed with glue water or calcined plaster and water makes a good putty for filling cracks in plastered ceilings. Frost-withstanding Mortar. Mortar made in the following manner will stand if used in almost all sorts of weather; 1 bushel of unslaked lime, 3 bushels of sharp sand, mix 1 pound of alum with 1 pint of linseed oil, and thoroughly mix this with the mortar when making it, and use hot. The alum will counteract the action of the frost on the mortar.
Fugitive Colors. Lakes and vermilions are very fugitive when exposed to the light, and an endeavor must be made to mix them so as to retain their beauty and natural color the longest possible time. Varnish containing no resin gum has been found by experience to extend their life and beauty the longest.
Gilding on Iron. The following directions are for putting on japan and gilding on ironwork: The articles to be japanned are clean of oil, usually by the use of turpentine, and the japan varnish applied, when the articles are placed in a hot oven to dry. To gild japanned articles, the part to be gilded is covered with oil size, thinned with turpentine, and gold powder put on with a puff. This is then ​varnished and moderately heated in an oven. Leaf gold may be applied in the same way.
Glass Window Writing. To mix colors: Mix dry fine colors with clear varnish or linseed oil, turpentine, and driers, also dry colors, gold size, and turpentine. By using dry colors a good body is obtained. As to background, use quick drying varnish and dry colors or gold size and turpentine, these will dry quickly. Rich brown: 2 parts black, 1 part yellow, 3 parts red, 3 parts turpentine, 1 part oil, a little gold size, and drier. Olive color: 16 parts lemon chrome, 2 parts Prussian blue, 2 parts lamp-black, 3 parts turpentine, to 1 part oil, driers, and gold size. For black letters get as much black as required, and mix with gold size and turpentine, turpentine mostly, to required thickness. Any other color can be treated in the same way. For background use pure white lead, and mix with maple varnish and turpentine, for cream color stain with lemon chrome and yellow ochre in oil and stipple with a new brush. Do not paint letters and background same day, or they will work into one another.
Green or Golden Color for Brass. The pleasing green or golden color generally to be found on the cheap and light brass articles of French manufacture can be easily produced at but trifling expense by the following means: 1+$^3$⁄$_4$ ounces of caustic soda and 1+$^1$⁄$_2$ ounces of milk sugar are dissolved in 1+$^3$⁄$_4$ pints of water and boiled for a quarter of an hour. The solution is as clear as water at first, but gradually acquires a dark yellow color. The vessel is next taken from the fire, placed on a wooden support, and 1+$^1$⁄$_2$ ounces of a cold concentrated solution of blue vitriol stirred in. A red precipitate of suboxide of copper is at once formed, and by the time the mixture cools to 167° Fahrenheit the precipitate will have settled. A suitable wooden sieve is placed in the vessel, and in this the polished articles are laid. In about a minute the sieve is lifted up to see how far the operation has gone, and at the end of the second minute ​the golden color is dark enough. The sieve and articles are now taken out, and the latter are washed and then dried in sawdust. If the brass is left longer in the copper solution, in a short time a fine green lustre is produced, becoming yellow at first and then bluish green. After, it turns green, then the well-known iridescent colors finally appear. To obtain uniform colors it is necessary that they be produced slowly, at temperatures between 135° and 170° Fahrenheit. The copper bath can be used repeatedly, and can be kept a long time, if bottled up tightly, without change. After it is exhausted it can be renewed by adding $^3$⁄$_8$ of an ounce of caustic soda, replacing the water that has evaporated, heating to boiling, and adding $^7$⁄$_8$ of an ounce of a cold solution of blue vitriol.
Harmonious Colors. A whole wall, ceiling, or other space should not be entirely covered over with rich ornament, and so also in a colored piece of drapery or other ornamental work, it is better to have some portion of it much less rich and of less complicated pattern than the rest, and in some cases to have only a border round a single ground destitute of any pattern, as it is apt to fatigue the eye when overloaded with an equal richness of detail throughout. This is still more important in a colored building, where, if the whole walls, columns, and other parts are covered with elaborate and colored patterns, the eye feels a want of repose, and the same when a building is covered entirely with sculptured ornament without color. The richly carved part not only requires an unsculptured portion in order that it shall not fatigue the eye, but is improved and set off by the contrast, and contrast is as necessary for effect in form, quantity of detail, position of lines, as it is in color. On this principle great effect is sometimes given to a colored pattern by having a portion of the composition on the wall of the building without any color at all, and for the same reason an expanse of wall in a room often looks well when painted with a single ​uniform ground surrounded by a rich pattern. Again, certain colors are better suited for some places than for others, and the brighter and more transparent for higher positions, and if the hangings of a room are scarlet, crimson with gold has a richer and better effect for chairs than scarlet and gold. A carpet may be darker than the general tone of the draperies, and some of its colors may be carried up by the walls or the curtains, but if the carpet is dark, the furniture shows better by being of a lighter hue. Red, or a light color, is better than blue for table covers, and though green is not recommended for daylight, it lights up well at night, when blue does not, and this then often appears black, or when of a light tone is scarcely to be distinguished from green. Much, however, may be done to give blue its proper effect, even by artificial light, either by placing a light tone of blue close to the darker one, or by interspersing it with white, which will often lead the eye to see the darker blue, and prevent its appearing black. This may be seen in some Persian carpets where two blues are used. And if some of these have too much green for daylight, they have a good effect at night, except when in excess. Dark green, like dark blue, looks darker by artificial light.
How to Use Glue. For glue to be properly effective it requires to penetrate the pores of the wood, and the more a body of glue penetrates the wood the more substantial the joint will remain. Glues that take the longest to dry are to be preferred to those that dry quickly, the slow drying being always the strongest, other things being equal. For general use, no method gives such good results as the following: Break the glue up small, put it into an iron kettle, cover the glue with water, and allow it to soak twelve hours. After soaking boil until done. Then pour it into an air-tight box, leave the cover off until cold, then cover up tight. As glue is required, cut out a portion and melt in the usual way. Expose no more of the made glue to the atmosphere for any length of time than is necessary, ​as the atmosphere is very destructive to made glue. Never heat made glue in a pot that is subject to the direct heat of a fire or a lamp. All such methods of heating glue cannot be condemned in terms too severe. Do not use thick glue for veneering or joints. In all cases work it well into the wood, in a similar manner to what painters do with paint. Glue both surfaces of the work, except in cases of veneering. Never glue hot wood, as the hot wood will absorb all the water in the glue too suddenly, and leave only a very little residue.
Inert Pigments. An inert pigment is one which, when mixed with oil, will have no chemical action upon it. It will have no chemical effect upon any other substance with which it is mixed, as for instance barytes, silica and gypsum. On the other hand, white lead, Prussian blue, and chrome yellow, are chemical colors, and are supposed to chemically affect the oil and some other pigments.
Killing the Smell of Paint. Place a vessel of burning charcoal in the center of the room and throw on it two or three handfuls of juniper berries. Shut the windows and doors close. Twenty-four hours afterwards the door may be opened, when it will be found that the smell of the paint has disappeared. This can be done without any injury to curtains and tapestries.
Making Plaster Set Quickly or Slowly. In order to make plaster set quickly, mix it with water into which a little sulphate of potash has been dissolved. To make it set slowly, mix it with fine slaked lime. The time of setting may be regulated by changing the relative quantities.
Manganese. The various compounds of manganese are perhaps more used than any other driers. Of these the black manganese contains most oxygen, but many regard it as less useful than umber, which contains considerable manganese, and also iron. Umber is thought by some to make a less sensitive oil, that is, a fluid oil, or varnish, which changes less on exposure to the cold. Both ​manganese and umber lose some of their substance in the oil, but to what extent manganese or iron soaps are formed with the oil acids is not known. Both umber and black manganese boiled with oil darken it.
Marbleizing Glass. One method of marbleizing glass consists in applying a mixture of varnish and oil to the surface of water of proper extent, and spraying or blowing upon the layer or film of oil and varnish dry colored powders to represent the mottled, speckled, veined, or other appearance of mottled or other stone. The glass is prepared by being coated upon one surface with varnish or japan, and is then placed upon the powder supported by the oily surfaced water, and the powder immediately adheres or fastens itself to the varnish or japan on the glass. The apparatus for distributing the color consists of a spraying device or distributor having a receptacle for the composition, which is introduced through a hole covered by a perforated cap. There is a diaphragm with holes or perforations, which are closed by a slide. This diaphragm separates the space containing the mixture from a passage or extension, the end of the casing of the passage being contracted sufficiently to fit upon the end of the bellows. To operate this device the receptacle is filled with the composition, the cap is secured in its place, and the slide lifted. The bellows are then operated, and the pressure of air drives the mixture in fine spray or drops upon the surface of the water. The device for applying the dry colors to the floating sheet or drops of oil and varnish is similar to that described, but in order that a number of colors may be sprayed or blown upon the floating oil and varnish at the same time, the receptacle is divided at the end into two or more parts, and a shaft, having agitators, is extended through them. The air is forced by bellows or other suitable means through perforations in the diaphragm. Caps cover the various chambers, etc., and are perforated to permit of the escape of the powder. In operation the air from the bellows or ​other source enters the perforations in the plate, and, passing through the chambers, causes the agitators to lift the powder and agitate it, and at the same time the air pressure forces the powder through the perforations in the cap in fine streams of dust, and of course by moving the distributor, the dust may be distributed upon the floating oil or varnish as may be desired. It is obvious that the design of the marble, stone, or other article is produced upon the floating body of oil and varnish before it is applied to the glass, and it is also obvious that by coating the surface of the glass with varnish or other adhesive material of a like nature, upon placing the same with the surface having the varnish or adhesive material down, so that it shall be brought in contact with the coloring matter held by the floating surface or layer of oil and varnish, the coloring matter will immediately adhere to the japan or other adhesive coating, and will thereby become fastened to the glass, so that upon the removal of the glass the design laid out upon the floating layer of japan and oil is removed from the water, together with such of the floating oil and japan as unites therewith. Of course the coloring or mottled or other appearance of any marble or other stone, or of any other material, may be reproduced upon the glass by this process, as it will only be necessary to change the dry colors to correspond to those of the stone or article to be imitated or copied.
Metallizing Wood. A new method of treating wood, which gives it the appearance of a piece of shining polished metal, with a surface so hard and smooth as to be susceptible of a high polish, is as follows: The wood is first steeped in a bath of caustic alkali for two or three days, according to its degree of permeability, at a temperature of between 165° and 197° Fahrenheit. It is then placed in a second bath of hydrosulphate of calcium, to which a concentrated solution of sulphur is added after some twenty-four to thirty-six hours. The third bath is one of acetate ​of lead, at a temperature of from 95° to 120° Fahrenheit, and in this latter the wood is allowed to remain from thirty to fifty hours. After being subjected to a thorough drying, it is in a condition for being polished with lead, tin, or zinc, as may be desired, finishing the process with a burnisher of either glass or porcelain, the appearance of the wood being in every respect that of polished metal, having, in fact, the semblance of a polished mirror, which is unaffected by moisture.
Moulding Composition. A composition for making good some slight portion of a defective moulding is made of powdered whiting with glue in solution worked into a paste, with a sufficiency of turpentine to destroy the brittleness, a little linseed oil may be added to prevent stickiness. The composition may be colored to suit the surroundings.
Moulding Wax. To prepare wax for taking moulds, put some common beeswax into an earthenware pot, place it over a slow fire, and when it is all melted stir into it a little white lead or plumbago, about 1 ounce of the lead to 1 pound of the wax. This mixture tends to prevent the mould from cracking when cooling, and from floating in the solution. It should be re-melted two or three times before using for the first time. Another kind is made thus: Melt carefully over a moderate fire 2 pounds of yellow beeswax, add 4+$^1$⁄$_2$ pounds of Venice turpentine, 2 ounces of lard, 1+$^3$⁄$_4$ pounds of purified bole, and mix thoroughly. Then gradually pour the mixture into a vessel containing water, and thoroughly knead several times with the hands. The wax should be melted at such a low temperature that no bubbles appear upon the melted surface.
Paint for Iron. The following are anticorrosive paints for iron: Take 10 per cent, of burnt magnesia, or even baryta or strontia, and mix it cold with ordinary linseed oil paint, and then enough mineral oil to envelope the alkaline earth, the free acid of the paint will be ​neutralized, while the iron will be protected by the permanent alkaline action of the paint. Iron to be buried in deep earth may be painted with a mixture of 100 parts of resin, 25 parts of gutta percha, and 50 parts of paraffin, to which 20 parts of magnesia and some mineral oil have been added.
Plumber's Solder. Mix 2 or 3 parts of lead and 1 part of tin. It must be free from zinc.
Polished Floors. These should be rubbed two or three times with linseed oil, and then polished every week with turpentine and beeswax. The oftener the oil is rubbed in to begin with, the darker the boards will be.
Preserving Painted Iron. A method of preventing paint from detaching itself in large flakes from iron surfaces is as follows: First wash the surface to be painted with soap and water, rinse and let dry. When dry, go over it with a stiff brush dipped in hot linseed oil. When this becomes tacky the paint can be applied. If the object is small, and of such a nature that heating will not hurt it, raise the temperature until a drop of oil brought into contact with it smokes. Go over the surface carefully with the raw oil, and let cool. It is now ready to receive the paint. With large objects which cannot be heated, the main point is to apply the oil as hot as possible, the nearer to boiling point the better. Objects thus painted will preserve the coat of color for an indefinite period, the paint being unaffected by heat or cold, excessive moisture or excessive dryness. Wood exposed to the weather may be treated with good results in the manner indicated.
Preserving Putty. Good putty is made to harden on exposure, and consequently cans should be kept closed, and a little water, or, better still, linseed oil, should be kept on top of putty in tubs, large cans, and barrels, to prevent a hard crust from forming. A putty that shows no signs of getting stuff or hard after being open and exposed, lacks an important element of value.
​Preventing Glue from Cracking. The addition of a little chloride of calcium to glue will prevent its cracking when exposed to considerable heat.
Putty for Polished Wood. Take a small quantity of white beeswax, melt it down, and, while liquid, mix with whiting, as it gets thick, keep adding boiled oil until you have it as you wish it, when using it, sheet the wood over solid, let stand until the next day, when you can remove the surplus by using No. $^1$⁄$_2$ sandpaper. It is easier and cheaper than the shellac, and can be levelled sooner, leaving nothing but the pores or grain of the wood filled, which is better than having the wood all stained up with the shellac.
Removing Iron Rust. Iron rust can be removed by salt mixed with lemon juice being rubbed on, or either place the article in a bowl containing kerosene oil or wrap it in a soft cloth well saturated with the oil, allow it to remain so for two days, and then scour the rusty spots with brick-dust. If very badly rusted, use salt melted with hot sulphuric acid, after scouring well, rinse in boiling water, and polish clean with soft flannel and a little sweet oil.
Removing Spots from Ceilings. A very simple remedy for removing rain spots or such caused by water soaking through ceilings, has been employed with good results. Take unslaked white lime, dilute with alcohol, and paint the spots with it. When the spots are dry, which ensues quickly, as the alcohol evaporates, and the lime forms a sort of insulating layer, painting can be done with size color, and the spots will not show through again.
Removing Oil Stains from Marble Statuary. Make a paste with fullers' earth and hot water, cover the spots with it, let it dry on, and the next day scour it off with soap. Another recipe is to take $^1$⁄$_4$ pound soft soap, $^1$⁄$_4$ pound powdered whiting, 1 ounce soda, piece of blue the size of a walnut. Boil all together for a quarter of an hour, and rub over the marble while hot. Leave it on for ​twenty-four hours at least, then wash off, and polish with a coarse flannel. The above quantity is quite enough for an ordinary mantelpiece.
Restoring Antique Furniture. To restore to their original appearance antique pieces of furniture which have become unsightly on account of too frequent varnishing or besmearing by unskilled hands, the following method should be employed: Take equal parts of strong alcohol and good oil of turpentine, and heat this mixture in a bottle by placing it in hot water. With this warm liquid paint the article, whereupon the old varnish will dissolve at once. The varnish is then removed by scraping and wiping, and the spreading, scraping, and cleaning is repeated as often as necessary until the surface has become entirely clean again, so that the object may be rendered glossy, or dull, as required. This process is especially recommended, since it does not change or attack the color of the wood, as is often the case if lye is used.
Rotten Stone. This is sometimes harsh and gritty, and the best way of trying it is to take a little between the teeth, when the least portion of grit may be detected. Careful workmen will always wash it before they use it. This is effected by stirring the fine powder in a considerable quantity of water, then allowing it to remain at rest for a few seconds, and pouring the water into a glazed earthen vessel, the powder which precipitates will be very fine and smooth, by washing the remainder, the whole of the finer parts may be separated from the grit.
Rust on Marble. To remove rust from marble, an operation which depends upon the solubility of iron sulphide in a solution of potassium cyanide, is thus effected: Clay is made into a thin paste with ammonium sulphide, and the rust spot smeared with the mixture, care being taken that the spot is only just covered. After a lapse of ten minutes, this paste is washed off and replaced by one consisting of white bole mixed with a solution of potassium cyanide, ​1 to 4, which is in its turn washed of after a lapse of about two and a half hours. Should a reddish spot remain after washing off the first paste, a second layer may be applied for about five minutes.
Securing Brass Letters to Glass. Every one who uses brass letters on glass windows, and knows how often they drop off from unequal expansion, or from the too energetic efforts of window cleaners, will find the following useful: Litharge 2 parts, white lead 1 part, boiled linseed oil 3 parts, gum copal 1 part. Mixed just before using, this forms a quick-drying and secure cement.
Size, or Mordant Varnish. One of the best mordants or sizes for signs or for work to be exposed to the weather, is called fat-oil size. It should be prepared as follows: Expose boiled linseed oil to a strong heat in a pan, when it begins to smoke, set fire to the oil, allow it to burn a moment, and then suddenly extinguish it by covering the pan. This will be ready for use, when cold, but will require thinning with a little turpentine.
Softening Putty. When ordinary putty becomes very hard, it may be softened for the purpose of easy removal by keeping it moist for a short time with caustic potash or soda, or if the putty be painted with nitric or muriatic acid it will be softened in about an hour.
Specks. These are liable to appear when varnish is allowed to skin over. Some varnishes will skin over although the can is constantly corked, and this skin being broken and mixing with the varnish will cause it to look sandy or seedy. The well-known common causes of specky work may be mentioned, dust or pumice powder upon the job, dirt present in the air, particularly liable in loosely or badly built shops during windy weather, and specks or lice in the varnish brush due to a variety of causes.
Sponges. New sponges should always be soaked in warm water for several hours before being used, and the water should be changed while it is at all colored. Feel ​the sponge all over before using, as frequently small portions of rock remain in it, the sharp points of which scratch the paint.
Strong Glue for Damp Places. For a strong glue which will hold in a clamp place, the following recipe works well: Take of the best and strongest blue enough to make a pint when melted. Soak this until soft, pour off the water as in ordinary glue-making, and add a little water if the glue is likely to be too thick. When melted add three tablespoonfuls of boiled linseed oil. Stir frequently, and keep up the heat till the oil disappears, which may take the whole day, and perhaps longer. If necessary, add water to make up for that lost by evaporation. When no more oil is seen, a tablespoonful of whiting is added and thoroughly incorporated with the glue.
Sulphate of Manganese. This is a pink-colored salt, useful, especially with zinc white, for exposure to sulphur gases. The following is the formula for its use: Sulphate of manganese 1 part, calcined sulphate of zinc 1 part, and acetate of manganese 1 part. These must be ground and sifted into a fine powder, and then dusted over 97 parts of zinc white. Another method for its use is: 6 to 8 ounces of sulphate of manganese to 100 pounds of ground zinc white paint, the powder thoroughly mixed with a portion of the paint, and this portion thoroughly mixed with the whole. Unless care is taken in the mixing, the work may be spotted.
Taking Grease out of Boards. Pipeclay and water mixed together until they form a thick paste, and spread over the part where there is a stain, will take out the grease very soon. Other plans are to cover the part thickly with dry fuller's earth, or a mixture may be made of 5 parts of fuller's earth to 1 part each of pearlash and soft soap with boiling water to make a paste, lay it on quite hot, and leave till dry, and then scour it with soap or silver sand and water. For simply making the boards a good color and ​to keep them free from insects, use the following mixture: $^1$⁄$_4$ pound of lime and $^3$⁄$_4$ pound of sand to $^1$⁄$_2$ pound of soft soap. Lay it on the boards and scrub it in well, wash it off with clean water, and make it as dry as possible. If ink should be spilt on boards, it may be removed by the application of muriatic acid, and afterwards simply washed. For painted boards, either on the floor or wainscoting, nothing better or more cleansing can be used than fuller's earth, with or without soap.
Testing Plaster of Paris. The method of testing the quality of plaster of Paris is by taking a small pinch of the powder between the finger and thumb and gently rubbing it, if small particles of it are felt, grit indicates that parts of the plaster have already absorbed water, and it is therefore unfit for use. The same test may be observed by taking a pinch of the powder again and placing the fingers under water, and then rubbing the same way as before. If, however, in both of these tests no grit is felt, and under water a thin creamy substance is found, which is easily rubbed off the fingers, the plaster is in a proper condition for use.
To Clean White Marble. Mix together $^1$⁄$_2$ pound of pearl-ash, $^1$⁄$_2$ pound of soft soap, and 1 pound of whiting. Boil them until they become as thick as paste, and let the mixture cool. Before it is quite cold spread it over the surface of the marble and leave it for at least a whole day. Use a soft water to wash it off, and rub it well with soft cloths. For black marble nothing is better than spirits of turpentine.
To Perforate Glass. In drilling glass, stick a piece of stiff putty or clay where the hole is required, and make a hole in the putty the size required, reaching down to the glass. Pour a little molten lead in the hole, and if the glass is not too thick, the piece will at once drop out.
To Polish Marble. To polish marble, such as table-tops, the following mode is followed by masons: With a piece ​of sandstone with a very fine grit rub the slab backward and forward, using very fine sand and water, till the marble appears, equally rough, and not in scratches, next use a finer stone and finer sand, till its surface appears equally gone over, then, with fine emery powder and a piece of felt or old bat wrapped around a weight, rub till all the marks left by the former process are worked out, and it appears with a comparative gloss on its surface. Afterwards finish the polish with putty powder and fine clean rags. As soon as the face appears of a good gloss, do not put any more powder on the rag, but rub it well, and in a short time it will appear as if fresh from the mason's hands.
To Remove Rust. A mixture of kerosene oil and emery powder rubbed on with a piece of cloth makes steel as bright as a button. But as prevention is better than cure, to prevent the formation of rust the bright steel should be painted with wax varnish, made by dissolving 1 part of solid paraffin in 15 parts of benzole. This is a much more cleanly application than such fatty compounds as white lead and oil, and is well suited for steel grates and similar goods.
Transparent Paints for Glass. Take for a blue pigment Prussian blue, for red crimson lake, for yellow Indian yellow, for brown burnt sienna, for black lamp-black, and for other shades a mixture of the appropriate colors. Rub them in a size made as follows: Venice turpentine 2 ounces, oil of turpentine 1 ounce, and apply with a brush. For temporary purposes, fine and brilliant colors are obtained by dissolving aniline dyes in white shellac varnish, but they are fleeting colors, and do not always pay for the trouble.
Useful Size. A useful preparatory size can be made by boiling a handful of the leaves of wormwood and two or three heads of garlic in a quart of water, until the liquid is reduced to one-half, then strain it through a cloth, and add half a handful of common salt, and nearly half ​a pint of vinegar. The design of this composition, usually employed in gilding looking-glass and picture frames, is to obviate the greasiness of the wood, and prepare it the better to receive the coats which are to be laid on, and to preserve it from the ravages of worms. When used it is mixed with a sufficient portion of good glue, boiling hot. In applying it to the gilding of plaster or marble, the salt must be left out of its composition, as, in damp situations, this would produce a white saline efflorescence on the surface of the gold.
Varnishes for Engravings, Paints, and Maps. A piece of plate glass is heated, and while yet warm a little wax rubbed over it, water is then poured over the plate, the moistened picture laid thereon and pressed closely down by means of a piece of filtering paper. When dry the picture is removed, and will be found to possess a surface of great brilliancy, which is not injured by the process of mounting. Boil Chio turpentine till brittle, then powder and dissolve in oil of turpentine. Canada balsam and clear white resin of each 6 ounces, oil of turpentine 1 quart, dissolve. Digest gum sandarach 20 parts, gum mastic 8 parts, camphor 1 part, with alcohol 48 parts. The map or engraving must previously receive one or two coats of gelatine.
Waterproof Glue. Dissolve $^1$⁄$_2$ ounce each of gum sandarach and mastic in 8 fluid ounces of strong alcohol, to which add ½ ounce of turpentine. Put the dissolved gums into a double glue-pot, add by degrees a hot thick solution of glue to which isinglass has been added, stir the whole over the fire until all the ingredients are thoroughly incorporated. Next strain through a cloth while hot, and it is ready for use. It may now be returned to the glue-pot, and $^1$⁄$_2$ ounce of very finely powdered glass added to it. It should be used quite hot. Take of shellac 3 parts, india-rubber 1 part by weight. Dissolve each separately in ether free from alcohol. It is best to do this in stoppered bottles and without heating, as the ether readily evaporates. ​When solution is complete, mix the two, and keep well stoppered for use.
Waterproof Wash for Lime. This may be made by mixing the powder from 3 parts rock quartz, 3 parts broken marble and sandstone, also 2 parts burned porcelain clay with 3 parts freshly slaked lime, still warm. In this way a wash is made which forms a silicate if often wetted, and becomes finally like stone. It is applied thickly to the surface, allowed to dry for a day, and the next day frequently wetted, which makes it waterproof.
Whitewash that will not Rub off. Mix up half a pailful of lime and water, ready to put on the wall, then take $^1$⁄$_4$ pint of flour, mix it with water, then pour on it a sufficient quantity of boiling water to thicken it, and pour it while hot into the whitewash, stir all well together, and it is ready for use.
Writing on Glass. To write on glass, or, as it is properly termed, to etch, as the letters are eaten out by an acid, either liquid hydrofluoric acid or hydrofluoric acid gas is required, according to the effect desired to produce. The former eats away the glass but leaves it clear, the latter gives the part operated upon, a ground-glass appearance. For the first way, clean a piece of glass, warm it, rub over with white wax or beeswax, and trace the letters with a needle or penknife, going down to the surface of the glass, make a wall of wax all round the edge of the glass, and pour on hydrofluoric acid, and leave for two or three hours, then clean with turpentine. To produce letters with a ground-glass appearance, place in a leaden dish 2 parts of powdered fluoride of calcium, pour on 3 parts of sulphuric acid, and with a stick mix into a paste. Prepare the glass as before, except that there is no need for a wall of wax around the edges, cover the leaden vessel with this piece of glass, and by warming the vessel gas will be evolved which will attack every clear part of the glass. The workman must be very careful indeed in using the acid, of the gas, the ​fumes, if breathed, are highly injurious, causing ulcers on the lungs, whilst drops of the acid on the skin will act like a red-hot iron, and produce very painful sores, which are not very easily healed. Opal can also be treated as described above, and the letters colored or enamelled afterwards, or china colors may be used and the opal fired. White letters on colored glass may be obtained by using flashed glass, and treating the flashed side with acid, which is soon eaten through, leaving the plain glass underneath.
Zinc Sheeting Paints. A very durable weather-resisting paint for zinc sheets is made by mixing oxide of zinc with a fluid silicate, such as water glass and potash and soda, to which the required pigments are added. The proportion should be about three-quarters of a pound of zinc white to every pound of silicate, with or without water. This zinc silicate paint becomes insoluble in water in about twenty-four hours. It is equally useful for interior and outside work, but it must not be applied to greasy surfaces, nor to old coats of paint. New zinc, not being oxidized, should first be prepared by the application of a solution of 1 part of soda in 10 parts of water, and then be thoroughly washed with water only. A quick drying, weather-resisting paint of dark color for zinc sheets is made by mixing 5 pounds of graphite with 1 gallon of vinegar. The oxidized surface of the zinc, previously well brushed, is painted with the above, one coat giving a sufficiently dark color. New sheet zinc, however, requires two coats, and must first be oxidized by the following application, which is not strong enough to cause any deterioration of the metal: 1 part each of chloride of copper, nitrate of copper, and sal ammoniac, dissolved in 64 parts of water, and 1 part of hydrochloric acid added to the solution.