consisting of lead and oxygen. Formerly it was ground finely in oil,
either pure or with admixture of white vitriol and added to the dark
oil paints. Litharge and sugar of lead are used to-day only rarely
as drying agents, having been displaced by the liquid manganese
siccatives, which are easy to handle. E. Ebelin, however, is of the
opinion that the neglect of the lead compounds has not been beneficial
to decorative painting. Where these mediums were used in suitable
quantities hard-drying coatings were almost always obtained. Ebelin
believes that formerly there used to be less lamentation on account of
tacky floors, pews, etc., than at the present time.
Doubtless a proposition to grind litharge into the oil again will not
be favorably received, although some old master painters have by no
means discarded this method.
Sugar of lead (lead acetate) is likewise used as a drier for oil paint.
While we may presume in general that a siccative acts by imparting its
oxygen to the linseed oil or else prepares the linseed oil in such
a manner as to render it capable of readily absorbing the oxygen of
the air, it is especially sugar of lead which strengthens us in this
belief. If, according to Leuchs, a piece of charcoal is saturated with
lead acetate, the charcoal can be ignited even with a burning sponge,
and burns entirely to ashes. (Whoever desires to make the experiment
should take 2 to 3 parts, by weight, of sugar of lead per 100 parts of
charcoal.) This demonstrates that the sugar of lead readily parts with
its oxygen, which though not burning itself, supports the combustion.
Hence, it may be assumed that it will also as a siccative freely give
off its oxygen.
Tormin reports on a siccative, of which he says that it has been found
valuable for floor coatings. Its production is as follows: Pour 1 part
of white lead and 1 1/2 parts each of litharge, sugar of lead and
red lead to 12 1/2 parts of linseed oil, and allow this mixture to
boil for 8 to 10 hours. Then remove the kettle from the fire and add
to the mixture 20 parts of oil of turpentine. During the boiling, as
well as during and after the pouring in of the oil turpentine, diligent
stirring is necessary, partly to prevent anything from sticking to the
kettle (which would render the drier impure) and partly to cause the
liquid mass to cool off sooner. After that, it is allowed to stand for
a few days, whereby the whole will clarify. The upper layer is then
poured off and added to the light tints, while the sediment may be used
for the darker shades.
If white vitriol (zinc sulphate or zinc vitriol) has been introduced
among the drying agents, this is done in the endeavor to create a
non-coloring admixture for the white pigments and also not to be
compelled to add lead compounds, which, as experience has shown, cause
a yellowing of white coatings to zinc white. For ordinary purposes,
Dr. Koller recommends to add to the linseed oil 2 per cent (by weight)
of litharge and 1/2 per cent of zinc vitriol, whereupon the mixture
is freely boiled. If the white vitriol is to be added in powder form,
it must be deprived of its constitutional water. This is done in
the simplest manner by calcining. The powder, which feels moist, is
subjected to the action of fire on a sheet-iron plate, whereby the
white vitriol is transformed into a vesicular, crumbly mass. At one
time it was ground in oil for pure zinc white coatings only, while for
the other pigments litharge is added besides, as stated above.
As regards the manganese preparations which are employed for
siccatives, it must be stated that they do not possess {637} certain
disadvantages of the lead preparations as, for instance, that of being
acted upon by hydrogen sulphide gas. The ordinary brown manganese
driers, however, are very liable to render the paint yellowish, which,
of course, is not desirable for pure white coatings. In case of too
large an addition of the said siccative, a strong subsequent yellowing
is perceptible, even if, for instance, zinc white has been considerably
“broken” by blue or black. But there are also manganese siccatives or
drying preparations offered for sale which are colorless or white, and
therefore may unhesitatingly be used in comparatively large quantities
for white coatings. A pulverulent drying material of this kind
consists, for example, of equal parts of calcined (i. e., anhydrous)
manganese vitriol, manganous acetate, and calcined zinc vitriol.
Of this mixture 3 per cent is added to the zinc white. Of the other
manganese compounds, especially that containing most oxygen, viz.,
manganic peroxide, is extensively employed. This body is treated as
follows: It is first coarsely powdered, feebly calcined, and sifted.
Next, the substance is put into wire gauze and suspended in linseed
oil, which should be boiled slightly. The weight of the linseed oil
should be 10 times that of the manganese peroxide.
According to another recipe a pure pulverous preparation may be
produced by treating the manganic peroxide with hydrochloric acid, next
filtering, precipitating with hot borax solution, allowing to deposit,
washing out and finally drying. Further recipes will probably be
unnecessary, since the painter will hardly prepare his own driers.
Unless for special cases driers should be used but sparingly. As a
rule 3 to 5 per cent of siccative suffices; in other words, 3 to 5
pounds of siccative should be added to 100 pounds of ground oil paint
ready for use. As a standard it may be proposed to endeavor to have
the coating dry in 24 hours. For lead colors a slight addition of
drier is advisable; for red lead, it may be omitted altogether. Where
non-tacky coatings are desired, as for floors, chairs, etc., as well as
a priming for wood imitations, lead color should always be employed as
foundation, and as a drier also a lead preparation. On the other hand,
no lead compounds should be used for pure zinc-white coats and white
lacquering.
«Testing Siccatives.»—Since it was discovered that the lead and
manganese compounds of rosin acids had a better and more rapid action
on linseed oil than the older form of driers, such as red lead,
litharge, manganese dioxide, etc., the number of preparations of the
former class has increased enormously. Manufacturers are continually
at work endeavoring to improve the quality of these compounds, and to
obtain a preparation which will be peculiarly their own. Consequently,
with such a large variety of substances to deal with, it becomes
a matter of some difficulty to distinguish the good from the bad.
In addition to the general appearance, color, hardness, and a few
other such physical properties, there is no means of ascertaining
the quality of these substances except practical testing of their
drying properties, that is, one must mix the driers with oil and
prove their value for oneself. Even the discovery of an apparently
satisfactory variety does not end the matter, for experience has shown
that such preparations, even when they appear the same, do not give
similar results. A great deal depends upon their preparation; for
example, manganese resinate obtained from successive consignments,
and containing the same percentage of manganese, does not always give
identical results with oil. In fact, variation is the greatest drawback
to these compounds. With one preparation the oil darkens, with another
it remains pale, or sometimes decomposition of the oil takes place in
part. The addition of a small proportion of drier has been known to
cause the separation of 50 per cent of the oil as a dark viscous mass.
One drier will act well, and the oil will remain thin, while with
another, the same oil will in the course of a few months thicken to the
consistency of stand oil. These various actions may all be obtained
from the same compound of rosin with a metal, the source only of the
drier varying.
The liquid siccatives derived from these compounds by solution in
turpentine or benzine also give widely divergent results. Sometimes
a slight foot will separate, or as much as 50 per cent may go to the
bottom of the pan, and at times the whole contents of the pan will
settle to a thick, jelly-like mass. By increasing the temperature, this
mass will become thin and clear once more, and distillation will drive
over pure unaltered turpentine or benzine, leaving behind the metallic
compound of rosin in its original state.
The compounds of metals with fatty acids which, in solution in
turpentine, have been used for many years by {638} varnish-makers,
show even greater variation. At the same time, a greater drying power
is obtained from them than from rosin acids, quantities being equal.
As these compounds leave the factory, they are often in solution in
linseed oil or turpentine, and undoubtedly many of the products of this
nature on the market are of very inferior quality.
The examination of these bodies may be set about in two ways:
_A._—By dissolving in linseed oil with or without heat.
_B._—By first dissolving the drier in turpentine and mixing the cooled
solution (liquid siccatives) with linseed oil.
Before proceeding to describe the method of carrying out the foregoing
tests, it is necessary to emphasize the important part which the
linseed oil plays in the examination of the driers. As part of the
information to be gained by these tests depends upon the amount of
solid matter which separates out, it is essential that the linseed
oil should be uniform. To attain this end, the oil used must always
be freed from mucilage before being used for the test. If this cannot
readily be obtained, ordinary linseed oil should be heated to a
temperature of from 518° to 572° F., so that it breaks, and should
then be cooled and filtered. With the ordinary market linseed oil,
the amount of solid matter which separates varies within wide limits,
so that if this were not removed, no idea of the separation of foot
caused by the driers would be obtained. It is not to be understood from
this that unbroken linseed oil is never to be used for ordinary paint
or varnish, the warning being only given for the sake of arriving at
reliable values for the quality of the driers to be tested.
_A._—_Solution of Drier in Linseed Oil._—The precipitated metallic
compounds of rosin (lead resinate, manganese resinate and lead
manganese resinate) dissolve readily in linseed oil of ordinary
temperature (60° to 70° F.). The oil is mixed with 1 1/2 per cent
of the drier and subjected to stirring or shaking for 24 hours, the
agitation being applied at intervals of an hour. Fused metallic
resinates are not soluble in linseed oil at ordinary temperatures,
so different treatment is required for them. The oil is heated in
an enameled pan together with the finely powdered drier, until the
latter is completely in solution, care being taken not to allow the
temperature to rise above 390° F. The pan is then removed from the fire
and its contents allowed to settle. The quantity of drier used should
not exceed 1 1/2 to 3 per cent. In the case of metallic linoleates
(lead linoleate, manganese linoleate and lead-manganese linoleate),
the temperature must be raised above 290° F. before they will go into
solution. In their case also the addition should not be greater than
3 per cent. Note, after all the tests have settled, the amount of
undissolved matter which is left at the bottom, as this is one of the
data upon which an idea of the value of the drier must be formed.
_B._—_Solution of Drier in Turpentine or Benzine._—For the preparation
of these liquid siccatives 1 to 1.4 parts of the metallic resinate or
linoleate are added to the benzine or turpentine and dissolved at a
gentle heat, or the drier may first be melted over a fire and added to
the solvent while in the liquid state. The proportion of matter which
does not go into solution must be carefully noted as a factor in the
valuation of the drier. From 5 to 10 per cent of the liquid siccative
is now added to the linseed oil, and the mixture shaken well, at
intervals during 24 hours.
Samples of all the oils prepared as above should be placed in small
clear bottles, which are very narrow inside, so that a thin layer of
the oil may be observed. The bottles are allowed to stand for 3 or
4 days in a temperate room, without being touched. When sufficient
time has been allowed for thorough settling, the color, transparency,
and consistency of the samples are carefully observed, and also the
quantity and nature of any precipitate which may have settled out. A
note should also be made of the date for future reference. Naturally
the drier which has colored the oil least and left it most clean and
thin, and which shows the smallest precipitate, is the most suitable
for general use. The next important test is that of drying power, and
is carried out as follows: A few drops of the sample are placed on a
clear, clean glass plate, 4 x 6 inches, and rubbed evenly over with
the fingers. The plate is then placed, clean side up, in a sloping
position with the upper edge resting against a wall. In this way any
excess of oil is run off and a very thin equal layer is obtained.
It is best to start the test early in the morning as it can then be
watched throughout the day. It should be remarked that the time from
the “tacky” stage to complete dryness is usually very short, so that
the observer must be constantly on the watch. If a good drier has been
used, the time may be from 4 to 5 hours, and should not be more than
12 or at the very highest {639} 15. The bleaching of the layer should
also be noted. Many of the layers, even after they have become as dry
as they seem capable of becoming, show a slight stickiness. These tests
should be set aside in a dust-free place for about 8 days, and then
tested with the finger.
«SIGN LETTERS:»
«To Remove Black Letters from White Enameled Signs».—It frequently
happens that a change has to be made on such signs, one name having to
be taken off and another substituted. Priming with white lead followed
by dull and glossy zinc white paint always looks like a daub and stands
out like a pad. Lye, glass paper or steel chips will not attack the
burned-in metallic enamel. The quickest plan is to grind down carefully
with a good grindstone.
SIGN-LETTER CEMENTS: See Adhesives, under Cements.
SIGNS, TO REPAIR ENAMELED: See Enamels.
«SILK:»
«Artificial “Rubbered” Silk.»—A solution of caoutchouc or similar
gum in acetone is added, in any desired proportion, to a solution of
nitro-cellulose in acetone, and the mixture is made into threads by
passing it into water or other suitable liquid. The resulting threads
are stated to be very brilliant in appearance, extremely elastic, and
very resistant to the atmosphere and to water. The product is not more
inflammable than natural silk.
«Artificial Ageing of Silk Fabrics.»—To give silk goods the appearance
of age, exposure to the sun is the simplest way, but as this requires
time it cannot always be employed. A quicker method consists in
preparing a dirty-greenish liquor of weak soap water, with addition of
a little blacking and gamboge solution. Wash the silk fabric in this
liquor and dry as usual, without rinsing in clean water, and calender.
«Bleaching Silk.»—The Lyons process of bleaching skeins of silk is
to draw them rapidly through a sort of aqua regia bath. This bath is
prepared by mixing 5 parts of hydrochloric acid with 1 of nitric,
leaving the mixture for 4 or 5 days at a gentle heat of about 77° F.,
and then diluting with about 15 times its volume of water. This
dilution is effected in large tanks cut from stone. The temperature
of the bath should be from 68° to 85° F., and the skeins should not
be in it over 15 minutes, and frequently not so long as that; they
must be kept in motion during all that time. When taken out, the silk
is immediately immersed successively in 2 troughs of water, to remove
every trace of the acid, after which they are dried.
Hydrogen peroxide is used as a silk bleach, the silk being first
thoroughly washed with an alkaline soap and ammonium carbonate to
free it of its gummy matter. After repeated washings in the peroxide
(preferably rendered alkaline with ammonia and soda), the silk is
“blued” with a solution of blue aniline in alcohol.
«Washing of Light Silk Goods.»—The best soap may change delicate
tints. The following method is therefore preferable: First wash the
silk tissue in warm milk. Prepare a light bran infusion, which is to
be decanted, and after resting for a time, passed over the fabric. It
is then rinsed in this water, almost cold. It is moved about in all
directions, and afterwards dried on a napkin.
SILK SENSITIZERS FOR PHOTOGRAPHIC PURPOSES: See Photography, under
Paper-Sensitizing Processes.
«Silver»
«Antique Silver» (see also Plating).—Coat the polished silver articles
with a thin paste of powdered graphite, 6 parts; powdered bloodstone, 1
part; and oil of turpentine. After the drying take off the superfluous
powder with a soft brush and rub the raised portions bright with a
linen rag dipped in spirit. By treatment with various sulphides an old
appearance is likewise imparted to silver. If, for example, a solution
of 5 parts of liver of sulphur and 10 parts of ammonium carbonate are
heated in 1 quart of distilled water to 180° F., placing the silver
articles therein, the latter first turn pale gray, then dark gray,
and finally assume a deep black-blue. In the case of plated ware, the
silvering must not be too thin; in the case of thick silver plating
or solid silver 1 quart of water is sufficient. The colors will then
appear more quickly. If the coloring is spotted or otherwise imperfect
dip the objects into a warm potassium cyanide solution, whereby the
silver sulphide formed is immediately {640} dissolved. The bath must
be renewed after a while. Silver containing much copper is subjected,
previous to the coloring, to a blanching process, which is accomplished
in a boiling solution of 15 parts of powdered tartar and 30 parts of
cooking salt in 2 pints of water. Objects which are to be mat are
coated with a paste of potash and water after the blanching, then dry,
anneal, cool in water, and boil again.
«Imitation of Antique Silver.»—Plated articles may be colored to
resemble old objects of art made of solid silver. For this purpose the
deep-lying parts, those not exposed to friction, are provided with a
blackish, earthy coating, the prominent parts retaining a leaden but
bright color. The process is simple. A thin paste is made of finely
powdered graphite and oil of turpentine (a little bloodstone or red
ocher may be added, to imitate the copper tinge in articles of old
silver) and spread over the whole of the previously plated article.
It is then allowed to dry, and the particles not adhering to the
surface removed with a soft brush. The black coating should then be
carefully wiped off the exposed parts by means of a linen rag dipped
in alcohol. This process is very effective in making imitations of
objects of antique art, such as goblets, candlesticks, vessels of every
description, statues, etc. If it is desired to restore the original
brightness to the object, this can be done by washing with caustic soda
or a solution of cyanide of potassium. Benzine can also be used for
this purpose.
«Blanching Silver.»—I.—Mix powdered charcoal, 3 parts, and calcined
borax, 1 part, and stir with water so as to make a homogeneous paste.
Apply this paste on the pieces to be blanched. Put the pieces on
a charcoal fire, taking care to cover them up well; when they have
acquired a cherry red, withdraw them from the fire and leave to cool
off. Next place them in a hot bath composed of 9 parts of water and 1
part of sulphuric acid, without causing the bath to boil. Leave the
articles in for about 1 hour. Remove them, rinse in clean water, and
dry.
II.—If the coat of tarnish on the surface of the silver is but light
and superficial, it suffices to rub the piece well with green soap
to wash it thoroughly in hot water; then dry it in hot sawdust and
pass it through alcohol, finally rubbing with a fine cloth or brush.
Should the coat resist this treatment, brush with Spanish white, then
wash, dry, and pass through alcohol. The employment of Spanish white
has the drawback of shining the silver if the application is strong
and prolonged. If the oxidation has withstood these means and if it
is desired to impart to the chain the handsome mat appearance of new
goods, it should be annealed in charcoal dust and passed through
vitriol, but this operation, for those unused to it, is very dangerous
to the soldering and consequently may spoil the piece.
«Coloring Silver.»—A rich gold tint may be imparted to silver articles
by plunging them into dilute sulphuric acid, saturated with iron rust.
«Frosting Polished Silver.»—Articles of polished silver may be frosted
by putting them into a bath of nitric acid diluted with an equal volume
of distilled water and letting them remain a few minutes. A better
effect may be given by dipping the article frequently into the bath
until the requisite degree of frosting has been attained. Then rinse
and place for a few moments in a strong bath of potassium cyanide;
remove and rinse. The fingers must not be allowed to touch the article
during either process. It should be held with wooden forceps or clamps.
«Fulminating Silver.»—Dissolve 1 part of fine silver in 10 parts of
nitric acid of 1.36 specific gravity at a moderate heat; pour the
solution into 20 parts of spirit of wine (85 to 90 per cent) and heat
the liquid. As soon as the mixture begins to boil, it is removed
from the fire and left alone until cooled off. The fulminic silver
crystallizes on cooling in very fine needles of dazzling whiteness,
which are edulcorated with water and dried carefully in the air.
«Hollow Silverware.»—A good process for making hollow figures
consists in covering models of the figures, made of a base or easily
soluble metal, with a thin and uniform coating of a nobler metal, by
means of the electric current in such a way that this coating takes
approximately the shape of the model, the latter being then removed by
dissolving it with acid. The model is cast from zinc in one or more
pieces, a well-chased brass mold being used for this purpose, and
the separate parts are then soldered together with an easily fusible
solder. The figure is then covered with a galvanized coating of silver,
copper, or other metal. Before receiving the coating of silver, the
figure is first covered with a thin deposit of copper, the silver being
added afterwards in the required thickness. But in order {641} that
the deposit of silver may be of the same thickness throughout (this is
essential if the figure is to keep the right shape), silver anodes,
so constructed and arranged as to correspond as closely as possible
to the outlines of the figure, should be suspended in the solution of
silver and cyanide of potassium on both sides of the figure, and at
equal distances from it. As soon as the deposit is sufficiently thick,
the figure is removed from the bath, washed, and put into a bath of
dilute sulphuric or hydrochloric acid, where it is allowed to remain
till the zinc core is dissolved. The decomposition of the zinc can be
accelerated by adding a pin of copper. The figure now requires only
boiling in soda and potassic tartrate to acquire a white color. If the
figure is to be made of copper, the zinc model must be covered first
with a thin layer of silver, then with the copper coating, and then
once more with a thin layer of silver, so that while the zinc is being
dissolved, the copper may be protected on either side by the silver.
Similar precautions must be taken with other metals, regard being paid
to their peculiar properties. Another method is to cast the figures,
entire or in separate parts, out of some easily fusible alloy in chased
metal molds. The separate portions are soldered with the same solder,
and the figure is then provided with a coating of copper, silver, etc.,
by means of the galvanic current. It is then placed in boiling water or
steam, and the inner alloys melted by the introduction of the water or
steam through holes bored for this purpose.