in rosins. Turpentine must be added always last to spirit varnish.
Turpentine in its clear recently distilled state will not mix with
alcohol, but must first be oxidized by exposing it to the air in an
uncorked bottle until a small quantity taken therefrom mixes perfectly
with alcohol. This usually takes from a month to six weeks. Mastic must
be added last of all to the ingredients of spirit varnish, as it is
not wholly soluble in alcohol but entirely so in a solution of rosins
in alcohol. Spirit varnishes that prove too hard and brittle may be
improved by the addition of either of the oils of turpentine, castor
seed, lavender, rosemary, or spike, in the proportion required to
bring the varnish to the proper temper.
«Coloring “Spirit” Varnishes.»—In modern works the following coloring
substances are used, separately and in blends: Saffron (brilliant
golden yellow), dragon’s blood (deep reddish brown), gamboge (bright
yellow), Socotrine or Bombay aloes (liver brown), asphalt, ivory, and
bone black (black), sandalwood, pterocarpus santalinus, the heartwood
(dark red), Indian sandalwood, pterocarpus indica, the heartwood
(orange red), brazil wood (dark yellow), myrrh (yellowish to reddish
brown; darkens on exposure), madder (reddish brown), logwood (brown),
red scammony rosin (light red), turmeric (orange yellow), and many
others according to the various shades desired.
«Manufacturing Hints.»—Glass, coarsely powdered, is often added to
varnish when mixed in large quantities for the purpose of cutting
the rosins and preventing them from adhering to the bottom and sides
of the container. When possible, varnish should always be compounded
without the use of heat, as this carbonizes and otherwise changes
the constituents, and, besides, danger always ensues from the highly
inflammable nature of the material employed. However, when heat is
necessary, a water bath should always be used; the varnish should never
fill the vessel over a half to three-fourths of its capacity.
«The Gums Used in Making Varnish.»—Juniper gum or true sandarac comes
in long, yellowish, dusty tears, and requires a high temperature
for its manipulation in oil. The oil must be so hot as to scorch a
feather dipped into it, before this gum is added; otherwise the gum
is burned. Because of this, juniper gum is usually displaced in oil
varnish by gum dammar. Both of these gums, by their dryness, counteract
the elasticity of oil as well as of other gums. The usual sandarac of
commerce is a brittle, yellow, transparent rosin from Africa, more
soluble in turpentine than in alcohol. Its excess renders varnish hard
and brittle. Commercial sandarac is also often a mixture of the African
rosin with dammar or hard Indian copal, the place of the African rosin
being sometimes taken by true juniper gum. This mixture is the pounce
of the shops, and is almost insoluble in alcohol or turpentine. Dammar
also largely takes the place of tender copal, gum anime, white amber,
white incense, and white rosin. The latter three names are also often
applied to a mixture of oil and Grecian wax, sometimes used in varnish.
When gum dammar is used as the main rosin in a varnish, it should
be first fused and brought to a boiling point, but not thawed. This
eliminates the property that renders dammar varnish soft and “tacky” if
not treated as above.
Venetian turpentine has a tendency to render varnish “tacky” and must
be skillfully counteracted if this effect is to be avoided. Benzoin
in varnish exposed to any degree of dampness has a {716} tendency to
swell, and must in such cases be avoided. Elemi, a fragrant rosin from
Egypt, in time grows hard and brittle, and is not so soluble in alcohol
as anime, which is highly esteemed for its more tender qualities. Copal
is a name given rather indiscriminately to various gums and rosins.
The East Indian or African is the tender copal, and is softer and more
transparent than the other varieties; when pure it is freely soluble
in oil of turpentine or rosemary. Hard copal comes in its best form
from Mexico, and is not readily soluble in oil unless first fused.
The brilliant, deep-red color of old varnish is said to be based on
dragon’s blood, but not the kind that comes in sticks, cones, etc.
(which is always adulterated), but the clear, pure tear, deeper in
color than a carbuncle, and as crystal as a ruby. This is seldom seen
in the market, as is also the tear of gamboge, which, mixed with the
tear of dragon’s blood, is said to be the basis of the brilliant orange
and gold varnish of the ancients.
Of all applications used to adorn and protect the surface of objects,
oil varnishes or lacquers containing hard rosins are the best, as they
furnish a hard, glossy coating which does not crack and is very durable
even when exposed to wind and rain.
To obtain a varnish of these desirable qualities the best old linseed
oil, or varnish made from it, must be combined with the residue left
by the dry distillation of amber or very hard copal. This distillation
removes a quantity of volatile oil amounting to one-fourth or one-fifth
of the original weight. The residue is pulverized and dissolved in hot
linseed-oil varnish, forming a thick, viscous, yellow-brown liquid,
which, as a rule, must be thinned with oil of turpentine before being
applied.
Hard rosin oil varnish of this sort may conveniently be mixed with
the solution of asphalt in the oil of turpentine with the aid of the
simple apparatus described below, as the stiffness of the two liquids
makes hand stirring slow and laborious. A cask is mounted on an axle
which projects through both heads, but is inclined to the axis of the
cask, so that when the ends of the axle are set in bearings and the
cask is revolved, each end of the cask will rise and fall alternately,
and any liquid which only partly fills the cask will be thoroughly
mixed and churned in a short time. The cask is two-thirds filled with
the two thick varnishes (hard rosin in linseed oil and asphalt in the
oil of turpentine) in the desired proportion, and after these have
been intimately mixed by turning the cask, a sufficient quantity of
rectified oil of turpentine to give proper consistence is added and the
rotation is continued until the mixture is perfectly uniform.
To obtain the best and most durable result with this mixed oil, rosin,
and asphalt varnish it is advisable to dilute it freely with oil of
turpentine and to apply 2 or 3 coats, allowing each coat to dry before
the next is put on. In this way a deep black and very glossy surface is
obtained which cannot be distinguished from genuine Japanese lacquer.
Many formulas for making these mixed asphalt varnishes contain
rosin—usually American rosin. The result is the production of a cheaper
but inferior varnish. The addition of such soft rosins as elemi and
copaiba, however, is made for another reason, and it improves the
quality of the varnish for certain purposes. Though these rosins
soften the lacquer, they also make it more elastic, and therefore more
suitable for coating leather and textile fabrics, as it does not crack
in consequence of repeated bending, rolling, and folding.
In coloring spirit varnish the alcohol should always be colored first
to the desired shade before mixing with the rosin, except where ivory
or bone black is used. If the color is taken from a gum, due allowance
for the same must be made in the rosins of the varnish. For instance,
in a varnish based on mastic, 10 parts, and tender copal, 5 parts, in
100 parts, if this is to be colored with, say, 8 parts of dragon’s
blood (or any other color gum), the rosins must be reduced to mastic,
8 parts, and tender copal, 4 parts. Eight parts of color gum are here
equivalent to 3 parts of varnish rosin. This holds true with gamboge,
aloes, myrrh, and the other gum rosins used for their color. This
seeming disproportion is due to the inert matter and gum insoluble in
alcohol, always present in these gum rosins.
«Shellac Varnish.»—This is made in the general proportion of 3 pounds
of shellac to a gallon of alcohol, the color, temper, etc., to be
determined by the requirements of the purchaser, and the nature of
the wood to which the varnish is to be applied. Shellac varnish is
usually tempered with sandarac, elemi, dammar, and the oil of linseed,
turpentine, spike, or rosemary.
Various impurities held in suspension in shellac varnish may be
entirely precipitated by the gradual addition of some {717} crystals
of oxalic acid, stirring the varnish to aid their solution, and then
setting it aside overnight to permit the impurities to settle. No more
acid should be used than is really necessary.
«Rules for Varnishing.»—1. Avoid as far as possible all manipulations
with the varnishes; do not dilute them with oil of turpentine, and
least of all with siccative, to expedite the drying. If the varnish has
become too thick in consequence of faulty storing, it should be heated
and receive an addition of hot, well-boiled linseed-oil varnish and oil
of turpentine. Linseed-oil varnish or oil of turpentine added to the
varnish at a common temperature renders it streaky (flacculent) and dim
and has an unfavorable influence on the drying; oil of turpentine takes
away the gloss of varnish.
2. Varnishing must be done only on smooth, clean surfaces, if a fine,
mirror-like gloss is desired.
3. Varnish must be poured only into clean vessels, and from these never
back into the stationary vessels, if it has been in contact with the
brush. Use only dry brushes for varnishing, which are not moist with
oil of turpentine or linseed oil or varnish.
4. Apply varnishes of all kinds as uniformly as possible; spread them
out evenly on the surfaces so that they form neither too thick nor too
thin a layer. If the varnish is put on too thin the coating shows no
gloss; if applied too thick it does not get even and does not form a
smooth surface, but a wavy one.
5. Like all oil-paint coatings, every coat of varnish must be perfectly
dry before a new one is put on; otherwise it is likely that the whole
work will show cracks. The consumer of varnish is only too apt to blame
the varnish for all defects which appear in his work or develop after
some time, although this can only be proven in rare cases. As a rule,
the ground was not prepared right and the different layers of paint
were not sufficiently dry, if the surfaces crack after a comparatively
short time and have the appearance of maps. The cracking of paint must
not be confounded with the cracking of the varnish, for the cracking
of the paint will cause the varnish to crack prematurely. The varnish
has to stand more than the paint; it protects the latter, and as it is
transparent, the defects of the paint are visible through the varnish,
which frequently causes one to form the erroneous conclusion that the
varnish has cracked.
6. All varnish coatings must dry slowly, and during the drying must be
absolutely protected from dust, flies, etc., until they have reached
that stage when we can pass the back of the hand or a finger over them
without sticking to it.
The production of faultless varnishing in most cases depends on the
accuracy of the varnisher, on the treatment of his brush, his varnish
pot, and all the other accessories. A brush which still holds the split
points of the bristles never varnishes clear; they are rubbed off
easily and spoil the varnished work. A brush which has never been used
does not produce clean work; it should be tried several times, and when
it is found that the varnishing accomplished by its use is neat and
satisfactory it should be kept very carefully.
The preservation of the brush is thus accomplished: First of all do not
place it in oil or varnish, for this would form a skin, parts of which
would adhere to it, rendering the varnished surface unclean and grainy;
besides these skins there are other particles which accumulate in the
corners and cannot be removed by dusting off; these will also injure
the work. In order to preserve the brush properly, insert it in a glass
of suitable size through a cork in the middle of which a hole has been
bored exactly fitting the handle. Into the glass pour a mixture of
equal parts of alcohol and oil of turpentine, and allow only the point
of the brush to touch the mixture, if at all. If the cork is air-tight
the brush cannot dry in the vapor of oil of turpentine and spirit. From
time to time the liquids in the glass should be replenished.
If the varnish remains in the varnish receptacle, a little alcohol
may be poured on, which can do the varnish no harm. At all events the
varnish will be prevented from drying on the walls of the vessel and
from becoming covered by a skin which is produced by the linseed oil,
and which indicates that the varnish is both fat and permanent. No
skin forms on a meager varnish, even when it drys thick.
After complete drying of the coat of varnish it sometimes happens
that the varnish becomes white, blue, dim, or blind. If varnish turns
white on exposure to the air the quality is at fault. The varnish is
either not fat enough or it contains a rosin unsuitable for exterior
work (copal). The whitening occurs a few days after the drying of the
varnish and can be removed only by rubbing off the varnish.
«Preventing Varnish from Crawling.»—Rub down the surface to be
varnished {718} with sharp vinegar. Coating with strongly diluted ox
gall is also of advantage.
«Amber Varnish.»—This varnish is capable of giving a very superior
polish or surface, and is especially valuable for coach and other
high-class work. The amber is first bleached by placing a quantity—say
about 7 pounds—of yellow amber in a suitable receptacle, such as an
earthenware crucible, of sufficient strength, adding 14 pounds of sal
gemmæ (rock or fossil salt), and then pouring in as much spring water
as will dissolve the sal gemmæ. When the latter is dissolved more water
is added, and the crucible is placed over a fire until the color of the
amber is changed to a perfect white. The bleached amber is then placed
in an iron pot and heated over a common fire until it is completely
dissolved, after which the melting pot is removed from the fire, and
when sufficiently cool the amber is taken from the pot and immersed in
spring water to eliminate the sal gemmæ, after which the amber is put
back into the pot and is again heated over the fire till the amber is
dissolved. When the operation is finished the amber is removed from the
pot and spread out upon a clean marble slab to dry until all the water
has evaporated, and is afterwards exposed to a gentle heat to entirely
deprive it of humidity.
«Asphalt Varnishes.»—Natural asphalt is not entirely soluble in any
liquid. Alcohol dissolves only a small percentage of it, ether a much
larger proportion. The best solvents are benzol, benzine, rectified
petroleum, the essential oils, and chloroform, which leave only a
small residue undissolved. The employment of ether as a solvent is
impracticable because of its low boiling point, 97° F., and great
volatility. The varnish would dry almost under the brush. Chloroform
is not open to this objection, but it is too expensive for ordinary
use. Rectified petroleum is a good solvent of asphalt, but it is not a
desirable ingredient of varnish because, though the greater part of it
soon evaporates, a small quantity of less volatile substances, which is
usually present in even the most thoroughly rectified petroleum, causes
the varnish to remain “tacky” for a considerable time and to retain a
disagreeable odor much longer. Common coal-tar benzine is also a good
solvent and has the merit of cheapness, but its great volatility makes
the varnish dry too quickly for convenient use, especially in summer.
The best solvent, probably, is oil of turpentine, which dissolves
asphalt almost completely, producing a varnish which dries quickly and
forms a perfect coating if the turpentine has been well rectified. The
turpentine should be a “water white,” or entirely colorless, liquid of
strong optical refractive power and agreeable odor, without a trace
of smokiness. A layer 1/5 of an inch in depth should evaporate in a
short time so completely as to leave no stain on a glass dish.
But even solutions of the best Syrian asphalt in the purest oil of
turpentine, if they are allowed to stand undisturbed for a long time in
large vessels, deposit a thick, semi-fluid precipitate which a large
addition of oil of turpentine fails to convert into a uniform thin
liquid. It may be assumed that this deposit consists of an insoluble or
nearly insoluble part of the asphalt which, perhaps, has been deprived
of solubility by the action of light. Hence, in order to obtain a
uniform solution, this thick part must be removed. This can be done,
though imperfectly, by carefully decanting the solution after it has
stood for a long time in large vessels. This tedious and troublesome
process may be avoided by filtering the solution as it is made, by
the following simple and quite satisfactory method: The solution is
made in a large cask, lying on its side, with a round hole about 8
inches in diameter in its upper bilge. This opening is provided with
a well-fitting cover, to the bottom of which a hook is attached. The
asphalt is placed in a bag of closely woven canvas, which is inclosed
in a second bag of the same material. The diameter of the double bag,
when filled, should be such as to allow it to pass easily through the
opening in the cask, and its length such that, when it is hung on the
hook, its lower end is about 8 inches above the bottom of the cask.
The cask is then filled with rectified oil of turpentine, closed, and
left undisturbed for several days. The oil of turpentine penetrates
into the bag and dissolves the asphalt, and the solution, which is
heavier than pure oil of turpentine, exudes through the canvas and
sinks to the bottom of the cask. Those parts of the asphalt which are
quite insoluble, or merely swell in the oil of turpentine, cannot pass
through the canvas, and are removed with the bag, leaving a perfect
solution. When all soluble portions have been dissolved, the bag, with
the cover, is raised and hung over the opening to drain. If pulverized
asphalt has {719} been used the bag is found to contain only a small
quantity of semi-fluid residue. This, thinned with oil of turpentine
and applied with a stiff brush and considerable force, forms a thick,
weather-resisting, and very durable coating for planks, etc.
The proportion of asphalt to oil of turpentine is so chosen as to
produce, in the cask, a pretty thick varnish, which may be thinned to
any desired degree by adding more turpentine. For use, it should be
just thick enough to cover bright tin and entirely conceal the metal
with a single coat. When dry, this coat is very thin, but it adheres
very firmly, and continually increases in hardness, probably because of
the effect of light. This supposition is supported by the difficulty
of removing an old coat of asphalt varnish, which will not dissolve in
turpentine even after long immersion, and usually must be removed by
mechanical means.
For a perfect, quick-drying asphalt varnish the purest asphalt must be
used, such as Syrian, or the best Trinidad. Trinidad seconds, though
better than some other asphalts, yield an inferior varnish, owing to
the presence of impurities.
Of artificial asphalt, the best for this purpose is the sort known as
“mineral caoutchouc,” which is especially suitable for the manufacture
of elastic dressings for leather and other flexible substances. For
wood and metal it is less desirable, as it never becomes as hard as
natural asphalt.
«FORMULAS:»
I.—A solution of 1 part of caoutchouc in 16 parts of oil of turpentine
or kerosene is mixed with a solution of 16 parts of copal in 8 parts of
linseed-oil varnish. To the mixture is added a solution of 2 parts of
asphalt in 3 or 4 parts of linseed-oil varnish diluted with 8 or 10
parts of oil of turpentine, and the whole is filtered. This is a fine
elastic varnish.
II.—Coal-tar asphalt, American asphalt, rosin, benzine, each 20 parts;
linseed-oil varnish, oil of turpentine, coal-tar oil, each 10 parts;
binoxide of manganese, roasted lampblack, each 2 parts. The solid
ingredients are melted together and mixed with the linseed-oil varnish,
into which the lampblack has been stirred, and, finally, the other
liquids are added. The varnish is strained through tow.
«Bicycle Varnish.»—This is a spirit varnish, preferably made by a cold
process, and requires less technical knowledge than the preparation of
fatty varnishes. The chief dependence is upon the choice of the raw
materials. These raw materials, copal, shellac, etc., are first broken
up small and placed in a barrel adapted for turning upon an axis, with
a hand crank, or with a belt and pulley from a power shaft. The barrel
is of course simply mounted in a frame of wood or iron, whichever is
the most convenient. After the barrel has received its raw material, it
may be started and kept revolving for 24 hours. Long interruptions in
the turning must be carefully avoided, particularly in summer, for the
material in the barrel, when at rest, will, at this season, soon form
a large lump, to dissolve which will consume much time and labor. To
prevent the formation of a semi-solid mass, as well as to facilitate
the dissolving of the gum, it would be well to put some hard, smooth
stones into the barrel with the varnish ingredients.
«Bicycle Dipping Varnish» (Baking Varnish).—Take 50 parts, by weight,
of Syrian asphalt; 50 parts, by weight, of copal oil; 50 parts, by
weight, of thick varnish oil, and 105 parts, by weight, turpentine oil,
to which add 7 parts, by weight, of drier. When the asphalt is melted
through and through, add the copal oil and heat it until the water is
driven off, as copal oil is seldom free from water. Now take it off the
fire and allow it to cool; add first the siccative, then the turpentine
and linseed oil, which have been previously thoroughly mixed together.
This bicycle varnish does not get completely black until it is baked.
«Black Varnishes.»—Black spirit lacquers are employed in the wood and
metal industries. Different kinds are produced according to their use.
They are called black Japanese varnishes, or black brilliant varnishes.
«Black Japanese Varnish.»—I.—Sculpture varnish, 5 parts; red acaroid
varnish, 2 parts; aniline black, 1/4 part; Lyons blue, .0015 parts.
If a sculpture varnish prepared with heated copal is employed, a black
lacquer of especially good quality is obtained. Usually 1 per cent of
oil of lavender is added.
II.—Shellac 4 parts
Borax 2 parts
Glycerine 2 parts
Aniline black 5 parts
Water 50 parts
Dissolve the borax in the water, add {720} the shellac, and heat
until solution is effected; then add the other ingredients. This is a
mat-black varnish.
«For Blackboards.»—For blackening these boards mix 1/2 liter (1.05
pints) good alcohol, 70 grams (1,080 grains) shellac, 6 grams (92
grains) fine lampblack, 3 grams (46 grains) fine chalk free from sand.
If red lines are to be drawn, mix the necessary quantity of red lead in
alcohol and shellac.
«Bookbinders’ Varnishes.»—
I II III IV V
Per Per Per Per Per
Cent Cent Cent Cent Cent
Shellac 14.5 6.5 13.5 6.3 8.3
Mastic 6.0 2.0 — — 1.1
Sandarac 6.0 13.0 — 1.3 1.1
Camphor 1.0 — 0.5 1.5 —
Benzoin — — — — 13.7
Alcohol 72.5 78.5 86.0 79.2 75.8
Scent with oil of benzoin, of lavender, or of rosemary. Other authors
give the following recipes:
VI VII VIII IX
Per Per Per Per
Cent Cent Cent Cent
Blond shellac 11.5 13.0 9.0 —
White shellac 11.5 — — —
Camphor — 0.7 — —
Powdered sugar — 0.7 — —
Sandarac — — 18.0 6.6
Mastic — — — 13.0
Venice turpentine — — 2.0 6.6
Alcohol 77.0 85.6 71.0 73.8
All solutions may be prepared in the cold, but the fact that mastic
does not dissolve entirely, must not be lost sight of.