Morning journal and courier., 1882-09-07
Fixing Co1ors on Pottery.

From Nature.l
 The art of fixing colors on pottery, M Lauth tells us, differs essentially from that which deals with the coloring of any other medium. There is required in the materials perfect adhesion, absolute resistance to at- mosphcric influences, and brilliancy which will make the colors seem part of the object itself As the colors must be subjected 10 a very high tenn perature, there must be elim- mated from the palette of the ceramic artist all organic coloring matter, and all the un- stable mineral colors he must have recourse to oxides metallic silicates, or to metals. And ths fxation of these colors is always the result of 8 chemical action, of combination which takes place at high temperature be- tween the body of the porcelain and the mat. ters used in it's decoration. Many different methods are used for the purpose, but they are divided into two great clssses-decoration at great heat and the decoration by muffie, an oven of a special kind. The former consists in applying to the porcelain coloring sub stances, which are fixed and developed at the same temperature as that at which the DOT celain is baked this is how the most value results are attained; as the enamel covers the color it assumes an extreme briliiancy and depth-it becomes part and parcel of the ob ject itself. This is how the magnificent blue of Sevres is obtained, as well as certain browns and blacks, and few other combina- tions. The colors may be either mixed on the paste or put upon the object when mold od, DerOro enamellng, or mixed on the object itself when complete; they may be also ap piled to porcelain already baked, which may be again baked at the higher temperature This is notably the process employed ct Serres for their blues. One of the most brilliant varieties of decoration at high tenn perature consists in what is called the pro, cess of pates d'application. This method consists in painting by the brush on porcelain unbaked or heated by successive and care fully adjusted applications very great thick ness is attained, by sculpturing which the ar tist can give the decoration remarkable fin- ish and value. The object is th en heated enameled and baked. It is different with the decoration accomplished by means of 8 muf- fe oven in this method the painting is al ways made on baked porcelain, and conse- quently on enamel, and the heat employed is relatively low. In this process there is necessary, in order to make the colors on the metals adhere, medium, which is called the fondant it is generally silicate, or siicate- borate of lead By raising the temperature, these bodies fused, attack the object, combine with it, and at the same time deter mine by that reaction the adhesion of the coior According to the nature of the fon- dants and colors, greater or less heat may be applied, and as certain colors are more sensitive than others it is frequently nscessa- ry to bake at successive fires of different temperatures The baking of colors by this process requires very great experience the absence of any instruments of precision is greatly felt, and there is no other means of ascertaining the temperature that prevails in the mufHe than to observe samples of DOT celain the changes of color which are under gone by certain preparations very sensitive to differences of temperature.