lead acetate, thoroughly washed with hot water, and freed from water
by working the precipitated oleate on a hot tile, is much to be
preferred to the lead plaster made by the present official process. The
time-honored method of boiling litharge, olive oil, and water is for
the requirements of the pharmacists most tedious and unsatisfactory.
Since in the beginning of the process, at least, a temperature higher
than that of 212° F. is required, the water bath cannot be employed,
and in the absence of this limiting device the product is usually
“scorched.” When the steam bath under pressure can be used this
objection does not apply. But the boiling process requires from 3 to
4 hours, with more or less attention, while the precipitation method
does not take over half an hour. Besides, true litharge is difficult to
obtain, and any other kind will produce unsatisfactory results.
The following is the process employed:
Lead oleate (Emplastrum plumbi):
Soap, granular and dried 100 parts
Lead acetate 60 parts
Distilled water, a sufficient quantity.
{563}
Dissolve the soap in 350 parts hot distilled water and strain the
solution. Dissolve the lead acetate in 250 parts hot distilled water
and filter the solution while hot into the warm soap solution, stirring
constantly. When the precipitate which has formed has separated, decant
the liquid and wash the precipitate thoroughly with hot water. Remove
the precipitate, let it drain, free from water completely by kneading
it on a warm slab, form it into rolls, wrap in paraffine paper, and
preserve in tightly closed containers.
Emplastrum adhesivum:
Rubber, cut in small pieces 20 parts
Petrolatum 20 parts
Lead plaster 960 parts
Melt the rubber at a temperature not exceeding 302° F., add the
petrolatum, and continue the heat until the rubber is dissolved. Add
the lead plaster to the hot mixture, continue the heat until it becomes
liquid; then let it cool and stir until it stiffens.
«Court Plaster or Sticking Plaster.»—I.—Brush silk over with a solution
of isinglass, in spirits or warm water, dry and repeat several times.
For the last application apply several coats of balsam of Peru. This is
used to close cuts or wounds, by warming and applying it. It does not
wash off until the skin partially heals.
II.—Isinglass, 1 part; water, 10 parts; dissolve, strain the solution,
and gradually add to it of tincture of benzoin, 2 parts; apply this
mixture gently warmed, by means of a camel’s-hair brush, to the
surface of silk or sarcenet, stretched on a frame, and allow each
coating to dry before applying the next one, the application being
repeated as often as necessary; lastly, give the prepared surface a
coating of tincture of benzoin or tincture of balsam of Peru. Some
manufacturers apply this to the unprepared side of the plaster, and
others add to the tincture a few drops of essence of ambergris or
essence of musk.
III. (Deschamps).—A piece of fine muslin, linen, or silk is fastened
to a flat board, and a thin coating of smooth, strained flour paste is
given to it; over this, when dry, two coats of colorless gelatin, made
into size with water, quantity sufficient, are applied warm. Said to be
superior to the ordinary court plaster.
«Coloring of Modeling Plaster.»—I.—If burnt gypsum is stirred up
with water containing formaldehyde and with a little alkali, and
the quantity of water necessary for the induration of the plaster
containing in solution a reducible metallic salt is added thereto, a
plaster mass of perfectly uniform coloring is obtained. The hardening
of the plaster is not affected thereby. According to the concentration
of the metallic salt solutions and the choice of the salts, the most
varying shades of color, as black, red, brown, violet, pearl gray,
and bronze may be produced. The color effect may be enhanced by the
addition of certain colors. For the production of a gray-colored gypsum
mass, for example, the mode of procedure is as follows: Stir 15 drachms
of plaster with one-fourth its weight of water, containing a few drops
of formaldehyde and a little soda lye and add 10 drops of a one-tenth
normal silver solution, which has previously been mixed with the amount
of water necessary for hardening the gypsum. The mass will immediately
upon mixing assume a pearl-gray shade, uniform throughout. In order to
produce red or copper-like, black or bronze-like shades, gold salts,
copper salts or silver salts, bismuth salts or lead salts, singly or
mixed, are used. Naturally, these colorings admit of a large number of
modifications. In lieu of formaldehyde other reducing agents may be
employed, such as solutions of sulphurous acid or hydrogen peroxide
with a little alkali. Metals in the elementary state may likewise be
made use of, e. g., iron, which, stirred with a little copper solution
and plaster, produces a brown mass excelling in special hardness, etc.
This process of coloring plaster is distinguished from the former
methods in that the coloration is caused by metals in the nascent
state and that a very fine division is obtained. The advantage of the
dyeing method consists in that colorings can be produced with slight
quantities of a salt; besides, the fine contours of the figures are
in no way affected by this manner of coloring, and another notable
advantage lies in the mass being colored throughout, whereby a great
durability of the color against outside actions is assured. Thus a
peeling off of the color or other way of becoming detached, such as by
rubbing off, is entirely excluded.
II.—Frequently, in order to obtain colored plaster objects, ocher or
powdered colors are mixed with the plaster. This method leaves much
to be desired, because the mixture is not always perfect, and instead
of the expected uniform color, blotches appear. Here is a more {564}
certain recipe: Boil brazil wood, logwood, or yellow wood, in water,
according to the desired color, or use extracts of the woods. When the
dye is cold mix it with the plaster. The dye must be passed through a
cloth before use. One may also immerse the plaster articles, medals,
etc., in this dye, but in this case they must be left for some time and
the operation repeated several times.
«Treatment of Fresh Plaster.»—Freshly plastered cement surfaces on
walls may be treated as follows:
The freshly plastered surface first remains without any coating for
about 14 days; then it is coated with a mixture of 50 parts water and
10 parts ammonia carbonate dissolved in hot water; leave this coat
alone for a day, paint it again and wait until the cement has taken on
a uniform gray color, which takes place as a rule in 12 to 14 days.
Then prime the surface thus obtained with pure varnish and finish the
coating, after drying, with ordinary varnish paint or turpentine paint.
«Plaster for Foundry Models.»—Gum lac, 1 part; wood spirit, 2 parts;
lampblack in sufficient quantity to dye.
Plaster from Spent Gas Lime.—Spent lime from gas purifiers, in which
the sulphur has been converted into calcium sulphate, by exposure to
weather, if necessary, is mixed with clay rich in alumina. The mixture
is powdered, formed into balls or blocks with water, and calcined at
a temperature below that at which the setting qualities of calcium
sulphate are destroyed. Slaked lime, clay, and sand are added to the
calcined product, and the whole is finely powdered.
«Plaster Mold.»—Nearly all fine grades of metals can be cast in plaster
molds, provided only a few pieces of the castings are wanted. Dental
plaster should be used, with about one-half of short asbestos. Mix the
two well together, and when the mold is complete let it dry in a warm
place for several days, or until all the moisture is excluded. If the
mold is of considerable thickness it will answer the purpose better.
When ready for casting, the plaster mold should be warmed, and smoked
over a gas light; then the metal should be poured in, in as cool a
state as it will run.
«Cleaning of Statuettes and Other Plaster Objects.»—Nothing takes the
dust more freely than plaster objects, more or less artistic, which
are the modest ornaments of our dwellings. They rapidly contract a
yellow-gray color, of unpleasant appearance. Here is a practical method
for restoring the whiteness: Take finely powdered starch, quite white,
and make a thick paste with hot water. Apply, when still hot, with a
flexible spatula or a brush on the plaster object. The layer should
be quite thick. Let it dry slowly. On drying, the starch will split
and scale off. All the soiled parts of the plaster will adhere, and be
drawn off with the scales. This method of cleaning does not detract
from the fineness of the model.
«Hardening and Toughening Plaster of Paris.»—I.—Plaster of Paris at
times sets too rapidly; therefore the following recipe for toughening
and delaying drying will be useful. To calcined plaster of Paris add 4
per cent of its weight of powdered marshmallow root, which will keep it
from setting for about an hour, and augment its hardness when set, or
double the quantity of marshmallow root powder, and the plaster will
become very firm, and may be worked 2 or 3 hours after mixing, and may
be carved and polished when hard. It is essential that these powders,
which are of different densities and specific gravities, should be
thoroughly mixed, and the plaster of Paris be quite fresh, and it must
be passed through fine hair sieves to ensure its being an impalpable
powder. To ensure thorough mixing, pass the combined powders through
the hair sieve three times. Make up with water sufficient for the
required model or models. Should any of the powder be left over it may
be kept by being put in an air-tight box and placed in a warm room.
The marshmallow root powder may be replaced by dextrin, gum arabic, or
glue. The material treated is suitable while yet in a soft state, for
rolling, glass-tube developing, making plates, etc.
II.—Plaster of Paris may be caused to set more quickly if some alum be
dissolved in the water used for rendering it plastic. If the gypsum
is first moistened with a solution of alum and then again burned, the
resulting compound sets very quickly and becomes as hard as marble.
Borax may be similarly employed. The objects may also be be treated
with a solution of caustic baryta. But it has been found that no
matter how deep this penetrates, the baryta is again drawn toward
the surface when the water evaporates, a portion efflorescing on the
outside, and only a thin layer remaining in the outer shell, where it
is converted into carbonate. This at the same time {565} stops up the
pores, rendering it impossible to repeat the operation. It was later
found that the whole mass of the cast might be hardened by applying
to it with a brush made of glass bristles, a hot solution of baryta.
To prevent separation of the crystallized baryta at the surface, the
object must be raised to a temperature of 140° to 175° F. To produce
good results, however, it is necessary to add to the plaster before
casting certain substances with which the baryta can combine. These are
silicic acid in some form, or the sulphates of zinc, magnesium, copper,
iron, aluminum, etc. With some of these the resulting object may be
colored. As it is, however, difficult to insure the production of
uniform tint, it is better when employing salts producing color, to mix
the plaster with about 5 per cent of quicklime, or, better, to render
it plastic with milk of lime, and then to soak the object in a solution
of metallic sulphate.
«Preservation of Plaster Casts.»—Upon complete drying, small objects
are laid for a short while in celluloid varnish of 4 per cent, while
large articles are painted with it, from the top downward, using a
soft brush. Articles set up outside and exposed to the weather are not
protected by this treatment, while others can be readily washed off and
cleaned with water. To cover 100 square feet of surface, 1 3/4 pints
of celluloid varnish are required.
«To Arrest the Setting of Plaster of Paris.»—Citric acid will delay the
setting of plaster of Paris for several hours. One ounce of acid, at a
cost of about 5 cents, will be sufficient to delay the setting of 100
pounds of plaster of Paris for 2 or 3 hours. Dissolve the acid in the
water before mixing the plaster.
«Weatherproofing Casts.»—I.—Brethauer’s method of preparing plaster
of Paris casts for resisting the action of the weather is as follows:
Slake 1 part of finely pulverized lime to a paste, then mix gypsum with
limewater and intimately mix both. From the compound thus prepared the
figures are cast. When perfectly dry they are painted with hot linseed
oil, repeating the operation several times, then with linseed-oil
varnish, and finally with white oil paint. Statues, etc., prepared in
this way have been constantly exposed to the action of the weather for
4 years without suffering any change.
II.—Jacobsen prepares casts which retain no dust, and can be washed
with lukewarm soap water by immersing them or throwing upon them in a
fine spray a hot solution of a soap prepared from stearic acid and soda
lye in ten times its quantity, by weight, of hot water.
«Reproduction of Plaster Originals.»—This new process consists in
making a plaster mold over the original in the usual manner. After the
solidification of the plaster the mass of the original is removed, as
usual, by cutting out and rinsing out. The casting mold thus obtained
is next filled out with a ceramic mass consisting of gypsum, 1 part;
powdered porcelain, 5 parts; and flux, 1 part. After the mass has
hardened it is baked in the mold. This renders the latter brittle and
it falls apart on moistening with water while the infusion remains as
a firm body, which presents all the details of the original in a true
manner.
PLASTER ARTICLES, REPAIRING OF: See Adhesives and Lutes.
PLASTER GREASE: See Lubricants.
PLASTER, PAINTS FOR: See Paints.
PLASTER OF PARIS, MOLDS FOR CASTING: See Casting.
PLASTIC COMPOSITIONS: See Celluloid and Matrix Mass.
PLASTER, IRRITATING: See Ointments.
PLATES, CARE OF PHOTOGRAPHIC: See Photography.
PLATINA, BIRMINGHAM: See Alloys, under Brass.
«Plating»
The plating of metal surfaces is accomplished in four different ways:
(1) By oxidation, usually involving dipping in an acid bath; (2) by
electrodeposition, involving suspension in a metallic solution, through
which an electric current is passed; (3) by applying a paste that
is fixed, as by burning in; (4) by pouring on molten plating metal
and rolling. For convenience the methods of plating are arbitrarily
classified below under the following headings:
1. Bronzing.
2. Coloring of Metals.
3. Electrodeposition Processes.
4. Gilding and Gold-Plating. {566}
5. Oxidizing Processes.
6. Patina Oxidizing Processes.
7. Platinizing.
8. Silvering and Silver-Plating.
9. Tinned Lead-Plating.
10. Various Recipes.
«BRONZING:»
«Art Bronzes.»—These are bronzes of different tints, showing a great
variety according to the taste and fancy of the operator.
I.—After imparting to an object a coating of vert antique, it is
brushed to remove the verdigris, and another coat is applied with
the following mixture: Vinegar, 1,000 parts, by weight; powdered
bloodstone, 125 parts, by weight; plumbago, 25 parts, by weight. Finish
with a waxed brush and a coat of white varnish.
II.—Cover the object with a mixture of vinegar, 1,000 parts, by
weight; powdered bloodstone, 125 parts, by weight; plumbago, 25 parts,
by weight; sal ammoniac, 32 parts, by weight; ammonia, 32 parts, by
weight; sea salt, 32 parts, by weight. Finish as above.
«Antique Bronzes.»—In order to give new bronze castings the appearance
and patina of old bronze, various compositions are employed, of which
the following are the principal ones:
I.—Vert Antique: Vinegar, 1,000 parts, by weight; copper sulphate,
16 parts, by weight; sea salt, 32 parts, by weight; sal ammoniac, 32
parts, by weight; mountain green (Sanders green), 70 parts, by weight;
chrome yellow, 30 parts, by weight; ammonia, 32 parts, by weight.
II.—Vert Antique: Vinegar, 1,000 parts, by weight; copper sulphate,
16 parts, by weight; sea salt, 32 parts, by weight; sal ammoniac, 32
parts, by weight; mountain green, 70 parts, by weight; ammonia, 32
parts, by weight.
III.—Dark Vert Antique: To obtain darker vert antique, add a little
plumbago to the preceding mixtures.
IV.—Vinegar, 1,000 parts, by weight; sal ammoniac, 8 parts, by weight;
potassium bioxalate, 1 part, by weight.
«Brass Bronzing.»—I.—Immerse the articles, freed from dirt and grease,
into a cold solution of 10 parts of potassium permanganate, 50 parts of
iron sulphate, 5 parts of hydrochloric acid, in 1,000 parts of water.
Let remain 30 seconds; then withdraw, rinse off, and dry in fine, soft
sawdust. If the articles have become too dark, or if a reddish-brown
color be desired, immerse for about 1 minute into a warm (60° C. or
140° F.) solution of chromic acid, 10 parts; hydrochloric acid, 10
parts; potassium permanganate, 10 parts; iron sulphate, 50 parts;
water, 1,000 parts. Treat as before. If the latter solution alone be
used the product will be a brighter dark yellow or reddish-brown color.
By heating in a drying oven the tone of the colors is improved.
II.—Rouge, with a little chloride of platinum and water, will form
a chocolate brown of considerable depth of tone and is exceedingly
applicable to brass surfaces which are to resemble a copper bronze.
«Copper Bronzing.»—I.—After cleaning the pieces, a mixture made as
follows is passed over them with a brush: Castor oil, 20 parts;
alcohol, 80 parts; soft soap, 40 parts; water, 40 parts. The day
after application, the piece has become bronzed; and if the time is
prolonged, the tint will change. Thus, an affinity of shades agreeable
to the eye can be procured. The piece is dried in hot sawdust, and
colorless varnish with large addition of alcohol is passed over it.
This formula for bronzing galvanic apparatus imparts any shade desired,
from Barbodienne bronze to antique green, provided the liquid remains
for some time in contact with the copper.
II.—Acetate of copper, 6 parts; sal ammoniac, 7 parts; acetic acid, 1
part; distilled water, 100 parts. Dissolve all in water in an earthen
or porcelain vessel. Place on the fire and heat slightly; next, with
a brush give the objects to be bronzed 2 or 3 coats, according to the
shade desired. It is necessary that each coat be thoroughly dry before
applying another.
«Bronzing of Gas Fixtures.»—Gas fixtures which have become dirty or
tarnished from use may be improved in appearance by painting with
bronze paint and then, if a still better finish is required, varnishing
after the paint is thoroughly dry with some light-colored varnish that
will give a hard and brilliant coating.
If the bronze paint is made up with ordinary varnish it is liable to
become discolored from acid which may be present in the varnish. One
method proposed for obviating this is to mix the varnish with about
5 times its volume of spirit of turpentine, add to the mixture dried
slaked lime in the proportion of about 40 grains to the pint, agitate
well, {567} repeating the agitation several times, and finally allowing
the suspended matter to settle and decanting the clear liquid. The
object of this is, of course, to neutralize any acid which may be
present. To determine how effectively this has been done, the varnish
may be chemically tested.
«Iron Bronzing.»—I.—The surface of a casting previously cleaned and
polished is evenly painted with a vegetable oil, e. g., olive oil, and
then well heated, care being taken that the temperature does not rise
to a point at which the oil will burn. The cast iron absorbs oxygen at
the moment when the decomposition of the oil begins, and a brown layer
of oxide is formed which adheres firmly to the surface and which may be
vigorously polished, giving a bronze-like appearance to the surface of
the iron.
II.—To give polished iron the appearance of bronze commence by cleaning
the objects, then subject them for about 5 minutes to the vapor of a
mixture of concentrated hydrochloric and nitric acids; then smear them
with Vaseline and heat them until the vaseline begins to decompose. The
result is a fine bronzing.
«Liquid for Bronze Powder.»—Take 2 ounces gum animi and dissolve in
1/2 pint linseed oil by adding gradually while the oil is being
heated. Boil, strain, and dilute with turpentine.
«Bronzing Metals.»—I.—The following composition is recommended for
bronzing metal objects exposed to the air: Mix about equal parts of
siccative, rectified oil of turpentine, caoutchouc oil, and dammar
varnish, and apply this composition on the objects, using a brush. This
bronze has been found to resist the influences of the weather.
II.—Cover the objects with a light layer of linseed oil, and then
heat over a coal fire, prolonging the heat until the desired shade is
reached.
III.—Expose the objects to be bronzed for about 5 minutes to the
vapors of a bath composed of 50 parts of nitric acid and 50 parts of
concentrated hydrochloric acid. Then rub the articles with vaseline and
heat until the vaseline is decomposed. The objects to be bronzed must
always be perfectly polished.
IV.—To bronze iron articles they should be laid in highly heated coal
dust; the articles must be covered up in the glowing dust, and the heat
must be the same throughout. The iron turns at first yellow, then blue,
and finally rather black. Withdraw the objects when they have attained
the blue shade or the black color; then while they are still hot, rub
them with a wad charged with tallow.
V.—For electrolytic bronzing of metals the baths employed differ from
the brass baths only in that they contain tin in solution instead of
zinc. According to Elsner, dissolve 70 parts, by weight, of cupric
sulphate in 1,000 parts of water and add a solution of 8 parts of
stannic chloride in caustic lye. For a positive pole plate put in a
bronze plate. The bath works at ordinary temperature.
VI.—A good bath consists of 10 parts of potash, 2 parts of cupric
chloride, 1 part of tin salt, 1 part of cyanide of potassium dissolved
in 100 parts of water.
VII.—Mix a solution of 32 parts of copper sulphate in 500 parts of
water with 64 parts of cyanide of potassium. After the solution has
become clear, add 4 to 5 parts of stannic chloride dissolved in potash
lye.
VIII.—Precipitate all soda from a solution of blue vitriol by phosphate
of sodium, wash the precipitate well, and dissolve in a concentrated
solution of pyrophosphate of copper. Also, saturate a solution of
the same salt with tin salt. Of both solutions add enough in such
proportion to a solution of 50 parts, by weight, of pyrophosphate of
sodium in 1,000 parts of water until the solution appears clear and of
the desired color. A cast bronze plate serves as an anode. From time to
time a little soda, or if the precipitate turns out too pale, copper
solution should be added.
«Tin Bronzing.»—The pieces are well washed and all grease removed;
next plunged into a solution of copperas (green vitriol), 1 part;
sulphate, 1 part; water, 20 parts. When dry they are plunged again into
a bath composed of verdigris, 4 parts; dissolved in distilled wine
vinegar, 11 parts. Wash, dry, and polish with English red.