which enter into their composition, are not colored, but they generally
blacken on exposure to light. It is easy, therefore, to blacken silver
and obtain its oxide; it is sufficient to place it in contact with a
sulphide, vapor of sulphur, sulphohydric acids, such as the sulphides
or polysulphides of potash, soda, dissolved in water and called _eau
de barège_. The chlorides play the same part, and the chloride of
lime in solution or simply Javelle water may be used. It is used hot
in order to accelerate its action. The bath must be prepared new for
each operation for two reasons: (1) It is of little value; (2) the
sulphides precipitate rapidly and give best effects only at the time of
their direct precipitations. The quantity of the reagent in solution,
forming the bath, depends upon the thickness of the deposit of silver.
When this is trifling, the oxidation penetrates the entire deposit
and the silver exfoliates in smaller scales, leaving the copper bare.
It is necessary, therefore, in this case to operate with dilute baths
inclosing only about 45 grains of oxidizant at most per quart. The
operation is simple: Heat the necessary quantity of water, add the
sulphide or chloride and agitate to effect the solution of the mixture,
and then at once plunge in the silver-plated articles, leaving them
immersed only for a few seconds, which exposure is sufficient to cover
it with a pellicle of deep black-blue silver. After withdrawing they
are plunged in clean cold water, rinsed and dried, and either left mat
or else polished, according to the nature of the articles.
Should the result not be satisfactory, the articles are brightened by
immersing them in a lukewarm solution of cyanide of potassium. The
oxide, the true name of which would be the sulphuret or chloruret, can
be raised only on an object either entirely of silver or silver plated.
II.—Rub the article with a mixture of graphite, 6 parts, and powdered
bloodstone, 1 part, moistened with oil of turpentine. Allow to dry and
brush with soft brushes passed over wax. Or else, brush with a soft
brush wet with alcoholic or aqueous platinic chloride solution of 1 in
20.
III.—Sulphurizing is effected with the following methods: Dip in a
solution heated to about 175° F., of potassium sulphide, 5 parts, by
weight; ammonium carbonate, 10 parts; water, 1,000 parts; or, calcium
sulphide, 1 to 2 parts; sal ammoniac, 4 parts; water, 1,000 parts. {584}
IV.—In the following solution articles of silver obtain a warm brown
tone: Copper sulphate, 20 parts, by weight; potassium nitrate, 10
parts; ammonium chloride, 20 parts. By means of bromine, silver
and silver alloys receive a black coloring. On engraved surfaces a
niello-like effect may be produced thereby.
«Oxidized Steel.»—I.—Mix together bismuth chloride, 1 part; mercury
bichloride, 2 parts; copper chloride, 1 part; hydrochloric acid, 6
parts; alcohol, 5 parts; and water, 5 parts. To use this mixture
successfully the articles to be oxidized must be cleaned perfectly and
freed from all grease, which is best accomplished by boiling them in
a soda solution or by washing in spirit of wine. Care should be taken
not to touch the article with the fingers again after this cleaning.
However clean the hand may be, it always has grease on it and leaves
spots after touching, especially on steel. Next the object is dipped
into the liquid, or if this is not possible the solution is applied
thin but evenly with a brush, pencil, or rabbit’s foot. When the liquid
has dried, the article is placed for a half hour in simple boiling
water. If a very dark shade is desired the process is repeated until
the required color is attained.
II.—Apply, by means of a sponge, a solution of crystallized iron
chloride, 2 parts; solid butter of antimony, 2 parts; and gallic acid,
1 part in 5 parts of water. Dry the article in the air and repeat the
treatment until the desired shade is reached. Finally rinse with water,
dry, and rub with linseed-oil varnish.
«Tinning by Oxidation.»—A dipping bath for tinning iron is prepared by
dissolving 300 parts, by weight, ammonia alum (sulphate of alumina and
sulphate of ammonia) and 10 parts of melted stannous chloride (tin
salt) in 20,000 parts of warm water. As soon as the solution boils,
the iron articles, previously pickled and rinsed in fresh water, are
plunged into the fluid; they are immediately covered with a layer
of tin of a beautiful dull-white color, which can be made bright by
treatment in a tub or sack. Small quantities of tin salt are added from
time to time as may be required to replace the tin deposited on the
iron. This bath is also well adapted for tinning zinc, but here also,
as with iron, the deposit is not sufficient to prevent oxidation of
the metal below. Larger articles tinned in this way are polished by
scratch brushing. In tinning zinc by this process, the ammonia alum may
be replaced by any other kind of alum, or aluminum sulphate may be used
alone; experience has shown, however, that this cannot be done with
iron, cast iron, or steel. If it is desired to tin other metals besides
iron and zinc in the solution which we have described, the battery must
be resorted to; if the latter is used, the above solution should be
applied in preference to any other.
«PATINA OXIDIZING PROCESSES:»
«Patina of Art Bronzes.»—For all patinas, whether the ordinary brown of
commerce, the green of the Barye bronzes, or the dark-orange tint of
the Florentine bronzes, a brush is used with pigments varying according
to the shade desired and applied to the metal after it is warmed.
Recipes are to be met with on every hand that have not been patented.
But the details of the operation are the important thing, and often the
effect is produced by a handicraft which it is difficult to penetrate.
I.—A dark tint may be obtained by cleaning the object and applying a
coat of hydrosulphate of ammonia; then, after drying it, by rubbing
with a brush smeared with red chalk and plumbago. The copper may
also be moistened with a dilute solution of chloride of platina
and warmed slightly, or still by plunging it in a warm solution of
the hydrochlorate of antimony. For the verde antique a solution is
recommended composed of 200 grams of acetic acid of 8° strength, the
same quantity of common vinegar, 30 parts, by weight, of carbonate of
ammonia; 10 parts, by weight, of sea salt; with the same quantities
of cream of tartar and acetate of copper and a little water. To obtain
the bronze of medals several processes afford a selection: For example,
the piece may be dipped in a bath consisting of equal parts of the
perchloride and the sesquiazotate of iron, warming to the evaporation
of the liquid, and rubbing with a waxed brush.
II.—Dissolve copper nitrate, 10 parts, by weight, and kitchen salt, 2
parts, in 500 parts of water and add a solution of ammonium acetate
obtained by neutralization of 10 parts of officinal spirit of sal
ammoniac with acetic acid to a faintly acid reaction, and filling up
with water to 500 parts. Immerse the bronze, allow to dry, brush off
superficially and repeat this until the desired shade of color has been
obtained. {585}
«A Permanent Patina for Copper.»—
Green.—
I.—Sodium chloride 37 parts
Ammonia water 75 parts
Ammonium chloride 37 parts
Strong wine vinegar 5,000 parts
Mix and dissolve. Apply to object to be treated, with a camel’s-hair
pencil. Repeat the operation until the desired shade of green is
reached.
Yellow Green.—
II.—Oxalic acid 5 parts
Ammonium chloride 10 parts
Acetic acid, 30 per cent dilution 500 parts
Mix and dissolve. Use as above indicated. The following will produce
the same result:
III.—Potassium oxalate, acid 4 parts
Ammonium chloride 16–17 parts
Vinegar containing 6 per cent of acetic acid 1,000 parts
IV.—Bluish Green.—After using the first formula (for green) pencil over
with the following solution:
Ammonium chloride 40 parts
Ammonium carbonate 120 parts
Water 1,000 parts
Mix and dissolve.
Greenish Brown.—
V.—Potassium sulphuret 5 parts
Water 1,000 parts
Mix and dissolve. With this, pencil over object to be treated, let dry,
then pencil over with 10 parts a mixture of a saturated solution of
ammonia water and acetic acid and 5 parts of ammonium chloride thinned
with 1,000 parts of water. Let dry again, then brush off well. Repeat,
if necessary, until the desired hue is attained.
Another Blue Green.—
VI.—Corrosive sublimate 25 parts
Potassium nitrate 86 parts
Borax 56 parts
Zinc oxide 113 parts
Copper acetate 220–225 parts
Mix and heat together on the surface of the object under treatment.
VII.—Brown.—The following is a Parisian method of producing a beautiful
deep brown:
Potassium oxalate, acid 3 parts
Ammonium chloride 15 parts
Water, distilled 280 parts
Mix and dissolve. The object is penciled over with this several times,
each time allowing the solution to dry before putting on any more. The
process is slow, but makes an elegant finish.
«Green Patina Upon Copper.»—To produce a green patina upon copper take
tartaric acid, dilute it half and half with boiling water; coat the
copper with this; allow to dry for one day and rub the applied layer
off again the next day with oakum. The coating must be done in dry
weather, else no success will be obtained. Take hydrochloric acid and
dilute it half and half with boiling water, but the hydrochloric acid
should be poured in the water, not vice-versa, which is dangerous. In
this hydrochloric acid water dissolve as much zinc as it can solve and
allow to settle. The clear liquid is again diluted half with boiling
water and the copper is coated with this a few times.
«Black Patina.»—Black patina is obtained by coating with tallow the
pieces to be oxidized and lighting with a rosin torch. Finally, wipe
the reliefs and let dry.
«Blue-Black Patina.»—Use a dilute solution of chloride of antimony
in water and add a little free hydrochloric acid. Apply with a soft
brush, allow the article to dry and rub with a flannel. If expense is
no object, employ a solution of chloride of palladium, which gives a
magnificent blue black. It is necessary, however, to previously clean
the articles thoroughly in a hot solution of carbonate of soda, in
order to remove the dirt and greasy matter, which would prevent the
patina from becoming fixed.
«Red Patina.»—The following is a new method of making a red patina,
the so-called blood bronze, on copper and copper alloys. The metallic
object is first made red hot, whereby it becomes covered with a coating
consisting of cupric oxide on the surface and cuprous oxide beneath.
After cooling, it is worked upon with a polishing plate until the black
cupric oxide coating is removed and the cuprous oxide appears. The
metal now shows an intense red color, {586} with a considerable degree
of luster, both of which are so permanent that it can be treated with
chemicals, such as blue vitriol, for instance, without being in the
least affected.
If it is desired to produce a marbled surface, instead of an even red
color, borax or some chemical having a similar action is sprinkled
upon the metal during the process of heating. On the places covered
by the borax, oxidation is prevented, and after polishing, spots of
the original metallic color will appear in the red surface. These can
be colored by well-known processes, so as to give the desired marbled
appearance.
«PLATINIZING:»
«Platinizing Aluminum.»—Aluminum vessels coated with a layer of
platinum are recommended in place of platinum vessels, when not exposed
to very high temperatures. The process of platinizing is simple,
consisting in rubbing the aluminum surface, previously polished, with
platinic chloride, rendered slightly alkaline. The layer of platinum
is made thicker by repeated application. Potash lye is carefully
added to a solution of 5 to 10 per cent of platinic chloride in water
till a slightly alkaline reaction is produced on filtering paper or
a porcelain plate by means of phenolphthalein. This solution must
always be freshly prepared, and is the best for the purpose. Neither
galvanizing nor amalgamating will produce the desired result. Special
care must be taken that the aluminum is free from iron, otherwise black
patches will arise which cannot be removed. Vessels platinized in this
way must not be cleaned with substances such as sea-sand, but with a 5
to 10 per cent solution of oxalic acid in water, followed by thorough
rinsing in water. These vessles are said to be specially suitable for
evaporating purposes.
«Platinizing Copper and Brass.»—I.—The articles are coated with a thin
layer of platinum in a boiling solution of platinum sal ammoniac, 1
part; sal ammoniac, 8 parts; and water, 40 parts, and next polished
with chalk. A mixture of equal parts of platinum sal ammoniac and
tartar may also be rubbed on the objects. Steel and iron articles can
be platinized with an ethereal solution of platinic chloride. For small
jewelry the boiling solution of platinic chloride, 10 parts; cooking
salt, 200 parts; and water, 1,000 parts, is employed, which is rendered
alkaline with soda lye. In this, one may also work with zinc contact.
II.—Heat 800 parts of sal ammoniac and 10 parts of platinum sal
ammoniac to the boiling point with 400 parts of water, in a porcelain
dish, and place the articles to be platinized into this, whereby they
soon become covered with a coating of platinum. They are then removed
from the liquid, dried and polished with whiting.
«Platinizing on Glass or Porcelain.»—First dissolve the platinum at a
moderate temperature in aqua regia, and next evaporate the solution to
dryness, observing the following rules: When the solution commences to
turn thick it is necessary to diminish the fire, while carrying the
evaporation so far that the salt becomes dry, but the solution should
not be allowed to acquire a brown color, which occurs if the heat is
too strong. The result of this first operation is chloride of platina.
When the latter has cooled off it should be dissolved in alcohol (95
per cent). The dissolution accomplished, which takes place at the end
of 1 or 2 hours, throw the solution gradually into four times its
weight of essence of lavender, then put into a well-closed flask.
For use, dip a brush into the solution and apply it upon the objects
to be platinized, let dry and place in the muffle, leaving them in the
oven for about one-half hour. In this operation one should be guided
as regards the duration of the baking by the hardness or fusibility
of the objects treated. The platinization accomplished, take a cotton
cloth, dipped into whiting in the state of pulp, and rub the platinated
articles with this, rinsing with water afterwards.
«Platinizing Metals.»—Following are several processes of platinizing on
metals:
It is understood that the metals to be covered with platinum must be
copper or coppered. All these baths require strong batteries.
I.—Take borate of potash, 300 parts, by weight; chloride of platina, 12
parts; distilled water, 1,000 parts.
II.—Carbonate of soda, 250 parts, by weight; chloride of platina, 10
parts; distilled water, 1,000 parts.
III.—Sulphocyanide of potash, 12 parts, by weight; chloride of platina,
12 parts; carbonate of soda, 12 parts; distilled water, 1,000 parts.
IV.—Borate of soda, 500 parts, by weight; chloride of platina, 12
parts; distilled water, 1,000 parts. {587}
«SILVERING, SILVER-PLATING, AND DESILVERING:»
See also Silvering by Oxidation, under Oxidation Processes, under
Plating.
«Antique Silver.»—There are various processes for producing antique
silver, either fat or oxidized:
To a little copal varnish add some finely powdered ivory black or
graphite. Thin with spirits of turpentine and rub with a brush dipped
into this varnish the objects to be treated. Allow to dry for an hour
and wipe off the top of the articles with some rag, so that the black
remains only in the hollows. If a softer tint is desired, apply again
with a dry brush and wipe as the first time. The coating of black will
be weaker and the shade handsomer.
«Britannia Silver-Plating.»—I.—The article should first be cleaned and
then rubbed by means of a wet cloth with a pinch of powder obtained by
mixing together: Nitrate of silver, 1 part; cyanide of potassium, 2
parts; chalk, 5 parts. Then wipe with a dry cloth, and polish well with
rouge to give brilliancy.
II.—By the electric method the metal is simply plunged into a hot
saturated solution of crude potassium carbonate, and the plating is
then done directly, using a strong electrical current. The potassium
carbonate solution dissolves the surface of the britannia metal and
thus enables the silver to take a strong hold on the article.
«To Silver Brass, Bronze, Copper, etc.»—I.—In order to silver copper,
brass, bronze, or coppered metallic articles, dissolve 10 parts
of lunar caustic in 500 parts of distilled water, and 35 parts of
potassium cyanide (98 per cent) in 500 parts of distilled water; mix
both solutions with stirring, heat to 176° to 194° F. in an enameled
vessel, and enter the articles, well cleansed of fat and impurities,
until a uniform coating has formed.
II.—Zinc, brass, and copper are silvered by applying a paste of the
following composition: Ten parts of silver nitrate dissolved in 50
parts of distilled water, and 25 parts of potassium cyanide dissolved
in distilled water; mix, stir, and filter. Moisten 100 parts of whiting
and 400 parts of powdered tartar with enough of the above solution to
make a paste-like mass, which is applied by means of a brush on the
well-cleaned objects. After the drying of this coating, rinse off, and
dry in sawdust.
III.—To silver brass and copper by friction, rub on the articles,
previously cleaned of grease, a paste of silver chloride, 10 parts;
cooking salt, 20 parts; powdered tartar, 20 parts; and the necessary
water, using a rag.
«Desilvering.»—I.—It often happens in plating that, notwithstanding all
precautions, some pieces have failed and it is necessary to commence
the work again. For removing the silver that has been applied, a rapid
method is to take sulphuric acid, 100 parts, and nitrate of potash, 10
parts. Put the sulphuric acid and the nitrate of potash (saltpeter)
in a vessel of stoneware or porcelain, heated on the water bath. When
the silver has been removed from the copper, rinse the object several
times and recommence the silvering. This bath may be used repeatedly,
taking care each time to put it in a stoppered bottle. When it has been
saturated with silver and has no more strength, decant the deposit,
boil the liquor to dryness, add the residue to the deposit, and melt in
a crucible to regenerate the metal.
II.—To dissolve the silver covering of a metallic object, a bath is
made use of, composed of 66 per cent sulphuric acid, 3 parts, and 40
per cent nitric acid, 1 part. This mixture is heated to about 176° F.,
and the objects to be desilvered are suspended in it by means of a
copper wire. The operation is accomplished in a few seconds. The
objects are washed and then dried in sawdust.
«To Silver Glass Balls and Plate Glass.»—The following is a method for
silvering the glass balls which are used as ornaments in gardens, glass
panes, and concave mirrors: Dissolve 300 parts of nitrate of silver and
200 parts of ammonia in 1,300 parts of distilled water. Add 35 parts
of tartaric acid dissolved in 4 times its weight of water. Dilute the
whole with 15,000 to 17,000 parts of distilled water. Prepare a second
solution containing twice the amount of tartaric acid as the preceding
one. Apply each of these solutions successively for 15 to 20 minutes
on the glass to be silvered, which must previously have been cleaned
and dried. When the silvering is sufficient, wash the object with hot
water, let dry, and cover with a brown varnish.
«Iron Silver-Plating.»—I.—Iron articles are plated with quicksilver
in a solution of nitrate of mercury before being silvered. The
quicksilver is then removed by heating to 572° F. The articles may
also be first tinned to economize the silver. Steel is dipped in
a mixture of {588} nitrate of silver and mercury, each dissolved
separately in the proportion of 5 parts, by weight, to 300 parts, by
weight, of water, then wiped to remove the black film of carbon, and
silvered till a sample dipped in a solution of blue vitriol ceases to
turn red. According to H. Krupp, articles made of an alloy of nickel,
copper, and zinc, such as knives, forks, spoons, etc., should be coated
electrically with nickel, put into a solution of copper like that used
for galvanic coppering, and then electroplated.
II.—A brilliant silver color may be imparted to iron (from which all
grease has been previously removed) by treating it with the following
solution: Forty parts, by weight, chloride of antimony; 10 parts, by
weight, powdered arsenious acid; and 80 parts levigated hematite are
mixed with 1,000 parts of 90 per cent alcohol and gently heated for
half an hour on a water bath. A partial solution takes place, and a
small cotton pad is then dipped in the liquid and applied with a gentle
pressure to the iron. A thin film consisting of arsenic and antimony is
precipitated, as described by Dr. Langbein, in his “Handbuch der galv.
Metallniederschläge.” The brilliancy of the effect depends upon the
care with which the iron has previously been polished.
«To Silver-Plate Metals.»—I.—Nitrate of silver, 30 parts, by weight;
caustic potash, 30 parts; distilled water, 100 parts. Put the nitrate
of silver into the water; one-quarter hour afterwards add the potash,
and, when the solution is done, filter. It is sufficient to dip the
objects to be silvered into this bath, moving them about in it for 1 or
2 minutes at most; then rinsing and drying in sawdust. It is necessary
to pickle the pieces before using the bath. To make the nitrate of
silver one’s self, take 30 parts of pure silver and 60 parts of nitric
acid, and when the metal is dissolved add the caustic potash and the
water.
II.—Kayser’s silvering liquid, which is excellent for all kinds of
metals, is prepared from lunar caustic, 11 parts; sodium hyposulphite,
20 parts; sal ammoniac, 12 parts; whiting, 20 parts; and distilled
water, 200 parts. The articles must be cleaned well.
«Mosaic Silver.»—This compound consists of tin, 3 parts, by weight;
bismuth, 3 parts; and mercury, 1 1/2 parts. The alloy of these metals
is powdered finely, thus forming a silvery mass used for imitation
silvering of metals, paper, wood, etc. In order to impart to metals,
especially articles of copper and brass, an appearance similar to
silver, they are made perfectly bright. The powder of the mosaic silver
is mixed with six times the volume of bone ashes, adding enough water
to cause a paste and rubbing this on the metallic surface by means
of a cork of suitable shape. In order to silver paper by means of
this preparation it is ground with white of egg, diluted mucilage, or
varnish, and treated like a paint.
«Pastes for Silvering.»—I.—Carbonate of lime, 65 parts; sea salt, 60
parts; cream of tartar, 35 parts; nitrate of silver, 20 parts. Bray
all in a mortar, not adding the carbonate of lime until the other
substances are reduced to a fine powder. Next, add a little water to
form a homogeneous paste, which is preserved in blue bottles away from
the light. For use, put a little of this paste on a small pad and rub
the article with it.
II.—Articles of zinc, brass, or copper may also be silver-plated by
applying to them a pasty mass of the following composition: First
dissolve 10 parts, by weight, of nitrate of silver in 50 parts, by
weight, of distilled water; also 25 parts, by weight, of potassium
cyanide in sufficient distilled water to dissolve it. Pour the two
together, stir well, and filter. Now 100 parts, by weight, of whiting
or levigated chalk and 400 parts, by weight, of potassium bitartrate,
finely powdered, are moistened with the above solution sufficiently to
form a soft paste, which may be applied to the objects, previously well
cleansed, with a brush. After this coating has dried well, rinse it
off, and dry the object in clean sawdust.