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How was Ruby and Mother-of-Pearl glass made?

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Bernard C:
Looking at examples of Walsh Ruby (now often called "Cranberry") and standard and green Mother-of-Pearl glass, I cannot help but be amazed at how they achieved this.

With all this glass there is a very thin and even translucent layer of either red or white opal glass on the inside.   Sometimes this is difficult to see, but it is particularly clear with some examples of Ruby Pompeian and stemmed Mother-of-Pearl vases, like the example shown by Jeannette Hayhurst in Glass of the '20s & '30s, p22, where the white opal inner layer does not extend into the crystal clear stem.

How was it made, and how was it kept so even?

Bernard C.  8)

Leni:
Got any pics of examples, Bernard?  I'd love to see just what you mean, although I can't answer the question as to how it's done! :shock:  :?

Leni

Frank:
After much rumination and reading and re-reading of the different possibilities I have to assume that the effect is achieved through exposing the glass to vapours of stannous chloride (90 parts) and Bismuth nitrate (10 parts). These vapours cause a very thin layer of glass to have a chemical change that alters the optical effects. A muffle furnace is used. Hodkin and Cousen (1924) state this approach is used for Favrille and Mother of Pearl effect glass.

Glen:
Not unlike Carnival Glass?

Glen

Frank:
Full text including enamelling:


--- Quote from: "Hodhin & Cousen, 1920" ---Iridescent Glass.—Beautiful colour effects are obtained in a very simple manner by exposing the surface of hot glass for a short time to the action of metallic salt vapours. By this means an extremely thin layer of glass on the surface of the material is subjected to chemical change. Light, falling on the surface, is partly destroyed, certain colours of the incident white ray being lost, due to a phenomenon known as interference. The reflected ray is complementary in colour to the colour destroyed, and the colour actually obtained depends upon the thickness of the attacked layer on the surface of the glass. This varies over the article, and as a result, no one colour is obtained, but the glass is given a delightful iridescent appearance. Most successful of all salts used for this purpose is stannous chloride (SnCl2), and this is uniformly employed, though other salts are added for the production of special effects. The following are typical mixtures used:
(1)   For ordinary effects—pure stannous chloride.
(2)   Blue shades—stannous chloride 80 parts, strontium nitrate 5,
barium chloride 15.
(3)   Red shades—stannous chloride 88, strontium nitrate 7, barium
chloride 5.
(4)   Opalescent effects—stannous chloride 90, bismuth nitrate 10.
The surface of the glass must be perfectly clean, and the results obtained depend upon the temperature and the time of action. In use, a special muffle furnace is employed with a deep vertical recess open


 
FIG. 251.—A MUFFLE FURNACE FOR PRODUCING IRIDESCENT GLASS.

near to the bottom (Fig. 251). Whilst the article of glassware is in the process of manufacture, that is, just before it is cracked off from the pipe or punty, it is heated to the required temperature (a red heat) at the working hole, and then held in the closed chamber of the muffle. Meanwhile an iron ladle has been heated, and into this is dropped the powder for producing iridescence, which is then thrust into the recess below the muffle. The heated salts vaporise and pass into the upper chamber, where attack takes place, finally passing away to the chimney. Variations of this method give the well-known ware on the market, such as “Favrile” glass, “mother-of-pearl” glass, etc. The best glasses to use for this purpose are crystal or fairly dark-coloured glasses.

“Lustring” of Glass.—A solution of a metallic resinate is made in an ethereal oil, such as lavender, rosemary, or light camphor oil. The article to be treated is dipped into this, or is painted over with a brush, dried, and heated, when a beautiful lustrous effect is produced.
The resinate may be obtained by adding metallic nitrates in correct amount to molten resin. A second mode of preparation is by mixing solutions of metallic salts with sodium resinate (obtained by boiling resin with a caustic soda solution), in which case the insoluble resinate is filtered off, dried, fused, and dissolved in oil. As examples of lustring solutions we may give:
(1)   Iron resinate 1 part, lead resinate 1, oil 2—reddish-brown effect.
(2)   Cobalt resinate 1, lead resinate 1, oil 2—grey lustre.
(3)   Manganese resinate 1, lead resinate 1, oil 2—brownish lustre.

Enamelling.—Two methods are in use for decorating the surface of glassware with colour. One is a cold process in which the colours are merely painted upon the glass surface with a brush and then quickly dried. Such designs may be easily scratched from the glass. In the second process designs are painted on as before, but after drying the glass is placed in a muffle furnace and brought for a short time to a red heat. Colours so burnt in are metallic oxides or salts, or in some cases the metals themselves, together with a suitable flux, such as is got by fusing a mixture of sand, red lead, and borax. As a medium for applying the powdered enamel a good varnish or lacquer is necessary. When the colouring medium is heated in the muffle it melts to form a true glaze on the surface of the glass. The following are some of the chief colouring agents used:
YELLOW: Barium chromate, lead chromate, uranium compounds, Naples yellow (an antimony-lead compound).
RED: Ferric oxide, chrome red (basic lead chromate).
BROWN: Ferric oxide, with zinc, nickel, and cobalt oxides as toning agents.
BLUE: Cobalt oxide, toned by the oxides of aluminium, zinc, or chromium.
BLACK: Cobalt oxide with ferric oxide, manganese dioxide, etc.
GREEN: Chromic oxide (with aluminium, cobalt, or iron.oxides for toning), copper oxide with potassium bichromate.
WHITE : Stannic oxide, zirconium oxide, or finely-ground porcelain.
The enamels may be of two classes, opaque colouring enamels or transparent enamels. For the opaque enamels suitable fluxes are: (1) Sand 30 parts, red lead 80 parts; or (2) sand 40 parts, red lead 70 parts, borax 20 parts. For red, brown, and light blue colours the flux is generally first melted, cooled by pouring into water, and finely ground, and then mixed with the colouring agent in the proportion of about thirty of flux to one of colour. In some cases the colouring agent is melted first with the flux, and the enamel then ground and applied. Examples of this class are:
GREEN: 30 sand, 80 red lead, 2 copper oxide, 0.2 potassium bichromate.
DARK BLUE: 30 sand, 80 red lead, 1 cobalt oxide.
BLACK: 30 sand, 80 red lead, 4 cobalt oxide, 2 copper oxide, 1 ferric oxide, 1 manganese dioxide.
For TRANSPARENT ENAMELS a suitable flux is 10 parts sand, 70 parts red lead, 20 parts boric acid, or for PURPLE colours 10 sand, 80 red lead, 40 borax. Characteristic transparent enamels previously melted together are:
RED : 10 sand, 70 red lead, 20 boric acid, 8 pyrolusite.
YELLOWISH-GREEN: 10 sand, 70 red lead, 20 boric acid, 4 copper oxide, 2 uranium oxide.
MEDIUM BLUE: 10 sand, 70 red lead, 20 boric acid, 2 cobalt oxide.
Other examples in which the flux is first made and then mixed with the colouring agent before applying to the glass are:
GREEN : 100 flux, 8 copper oxide.
SKY BLUE: 100 flux, 1.5 cobalt oxide, 9 aluminium hydroxide (with addition of some chromic oxide when a green shade is desired).
For METALLIC SILVER EFFECTS finely divided silver (8 to 10 parts), and lead borate (1 part) are used, with, in some cases, addition of a small amount of basic bismuth nitrate. Silver carbonate may be employed in place of metallic silver. GILDING is performed similarly with a suitable gold preparation.
The so-called "yellow etch " consists of a finely divided silver compound, such as the chloride mixed thoroughly with yellow ochre. The etch is painted on the glass surface and burnt in, in a muffle furnace, when a yellow colouration of the glass is obtained. Gold and copper compounds may be similarly employed. In the case of copper, the oxide or sulphate is employed, and several firings used, the last being under reducing conditions, when a red etch is obtained.
VIGNETTING is usually done by first covering the glass to be decorated with a coat of dilute water-glass solution applied by means of a rubber stamp. Bronze powder, aluminium or agate is then dusted over, adheres to the glass, and is burnt in, giving a bronze, silvery or white effect respectively.

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