TECHNICAL INFORMATION ON BUILDING MATERIALS

TIBM - 4g

FOR USE IN THE DESIGN OF LOW-COST HOUSING

THE NATIONAL BUREAU OF STANDARDS

UNITED STATES DEPARTMENT OF COMMERCE

WASHINGTON, D. C.

June 5. 19^7

SHELLAC

Tlii s is chiefly a digest of sections of applicable Federal Specifications^- and National Bureau of Standards oublication, Technologic Paper

T232 "Shellac", (March 12, 1923),^ hy Percy H. Walker and Lawrence L.

Steel, covering basic materials, ureparation, grades, orange shellac,

bleached shellac, and shellac varnish.

Basic Materials

Lac Resin : Lac or lac resin, the driecl assimilated sap excreted

by generations of the East Indian insect "Tacchardia Lacca" on the twigs

of various species of trees on which they feed and propagate, is the

primary basic material from which shellac is produced.

Stick Lac : Lac resin incrusted twigs broken into short pieces

are the stick lac of commerce.

-^•Specifications adopted by the Federal Specifications Executive

Committee andapproved by the Director of Procurement, Treasury Department, for use of all departments and establishments of the Government.

Copies of all Federal Specifications mentioned in this digest may be

obtained from the Superintendent of Documents, Washington, D. C.

(Price 5 cents)

pAvailable from the Superintendent of Documents, Washington, D. C.

(Price 5 cents)

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06053 7-C
Seed or Grain Lac is stick lac. crushed into small granules,

about the size of wheat. The granules, ruby-red in color, are washed with water to remove a portion of the dye, and then screened

to remove as much of the twigs and bark as possible.

Garnet Lac , a dark colored nroduct, is usually made from the

impure lac residue remaining in the cloth bag 'used in producing

flake shellac. Sand and other impurities are usually eliminated by

dissolving the impure lac in alcohol or a dilute sodium carbonate

solution, and filtering. The alcohol is either driven off or the

lac is liberated from the alkaline solution by acid, and then fused

into lumps of various sizes. Button lac is essentially shellac fused

into a mass the shape of a button.

Preparation

Shellac is usually made by melting dry seed lac with up to 0.7$

arsenic sulphide (orpiment), with or without the addition of small

amounts of rosin, in long narrow cloth bags over a charcoal fire.

The softened lac mixture squeezed through the cloth by twisting the

bag, is resoftened and stretched into thin sheets, which, after cooling, are broken into the familiar shellac flakes of commerce.

Grades

Grading of shellac is based upon freedom from rosin and dirt,

and upon color of the flakes. Rosin is the most common adulterant

of shellac, especially because it greatly facilitates the melting

of seed lac, and also because of its low price.

Orange Shellac

Properties

;

Orange shellac is available both in the dry form

(flake, seed, or grain) and. in solution in alcohol (shellac varnish).

Specific gravity varies from 1.196 to 1.217, owing to minute air

bubbles inclosed during the manufacturing process. The softening

point is indefinite, and decomposition starts if shellac is heated

much above 100°C. It is insoluble in dilute mineral acids, and quite

insoluble in petroleum hydrocarbons and turpentine (a property possessed to the same degree by no other common resin soluble in alcohol).

It dissolves in ammonia or solutions of sodium carbonate, borax, and

other alkalies, and with the exception of a small amount of natural wax and mineral matter; it also dissolves in cold methyl or ethyl

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alcohol or in a mixture of these two (denatured alcohol), isouropyl,

and amyl alcohols (fusel oil). High-proof alcohol- must he used.

Ethyl or denatured alcohol much weaker than 95$ "by volume does not

dissolve shellac perfectly. Orange shellac is very stable and does

not depreciate in quality even during long storage.

The apparent light color of some samples of orange shellac may

he misleading where such effect is caused by air bubbles or the use of orpiment. When the samples are dissolved in alcohol, the orpiment

tends to slowly settle; the inclosed air bubbles are released; and

the resulting solution may be darker than the solution of a flake

shellac containing less inclosed air and orpiment and apparently of

a darker shade when in flake form.

Federal Specification: Specification TT-S-271 "Shellac; Orange"

covers four types (A,B,C, and D) of orange shellac for use in shipbottom paints and in the preparation of orange shellac varnish.

Tvne A , in general, includes the grades of shellac known in the

trade as "Double triangle G" , "Diamond I", "Superfine", the so-called

machine-made shellacs such as "CV" and "CYT1T", and the highest grades

"D.C. " and "V.S.O."

Type 3 , in general, includes the grades considered in the trade

as lower than " suoerfine" , but higher than pure "T.1T.", such as "Fine",

"Good", and "Heart".

Tyne C represents the grade known in the trade as "pure T .IT.

which is rosin-free, but darker and containing more insoluble material

than types A or B.

Tyne D represents the grade known in the trade as "TJ.S.S.A.T.U."

It usually contains up to a maximum of 3$ rosin, and, in addition,

it contains more insoluble material and is generally darker than types

A or B, but is usually a little lighter in color than type C.

Orange shellac, to meet this specification, must be the manufactured

product of stick lac freed from most of the lac dye and nreuared in

flake form. Seed, garnet, and button lac are not permissible.

Bleache d She 1 1 ac

Bleached shellac is produced by dissolving orange shellac in a dilute sodium carbonate solution, and then bleaching the solution

with a sodium hypochlorite, solution which destroys the red lac dye.

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The bleached shellac is then precipitated by mineral acid as an amorphous yellowish-white mass. Bleached shellac (white shellac),

prepared by this process, is quite sensitive to heat and must be

dried with care at rather low temperatures, or it may become

partially or wholly insoluble in alcohol. When stored for a. time,

bleached shellac tends to become more or less insoluble in alcohol.

Shellac Varnish

Preparation

;

Shellac varnish is produced by "cutting" (dissolving)

dry orange or bleached shellac in high-proof alcohol. The weighed

shellac in dry form should stand overnight in a closed vessel containing the proper volume of 190°-proof alcohol,-'- and then be stirred at

intervals until all lumas disappear. Mechanical stirring devices

are used for this purpose in factories manufacturing such products.

Properties ; The resistance of a dried film of shellac varnish

to turpentine and turpentine substitute (mineral spirits) is of great

value where the shellac is used as a first coating to fill the pores

of ivood, and to cover resinous knots and streaks, because any varnish

or wax polish subsequently apulied does not soften the shellac. This

valuable property is not possessed by most commercial so-called shellac

substitutes. Shellac varnish is not suitable for outside exposures,

as the dried film does not possess the wateroroof qualities and re- sistance to weather of a good long-oil spar varnish.

Shellac varnish dries only through evaporation of the solvent.

In humid weather the rapid evaporation of alcohol from the film may

lower the temperature sufficiently to cause moisture condensation.

This may turn the film white temporarily, but eventually the coating

should dry to its normal color.

Pederal Specification ; Specification TT-V-91 "Varnish; Shellac"

is intended to cover all needs of the Government for shellac varnish,

which shall be furnished as "Orange", Type I or II, and as "Bleached",

Tyne I or II. Each type shall also be furnished as light, medium, or heavy body as specified. The shellac varnish shall be made by "cutting"

the specified tyue of shellac in 95$ specially denatured alcohol,

United States Internal Revenue Bureau Formula Mo. 1.

Uhile pure l

cl0 o -proof alcohol may be used, a special denatured

alcohol which consists of 100 gallons of ethyl alcohol 190°-proof and

five gallons of approved wood alcohol, is commonly used.

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Orange Shellac Varnish

Tyne I , in general, includes the rosin-free meterial and the

lighter colored varnishes. Tyne II is intended for use where the

nresence of small percentages of rosin (not over 3/0 is not objectionable and where lightness of color is not essential.

Bleached Shellac Varnish 0 Type I , in general, will fulfill all

needs for a white shellac varnish. Type II will only be used in cases

where a clear bleached varnish, practically free from wax or other

suspended matter, is necessary.

1 Sometimes called "^hite shellac varnish".

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