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- Acid etching
- To stain and to lustre
- (Sand) Blasting
- Decals for decoration


is a way to dye the surface of a piece of glass. It is a chemical process that changes the surface layer of the glass.

In the book Glas by Steenberg-Simmingsköld the process is described (p 361, my translation):
"   Yellow transparent colour on a glass surface is obtaind by applying a paste, containing, among other substances, silver salts. The object is then subjected to heat. During the firing silver ions will migrate into the surface, replacing alcaline ions in the surface. The result of this process will vary with the composition of the glass, for instance the proportions between sodium and potassium. The firing is done at a relatively low temperature (ca 450 oC). Red stain is the result of copper salts and firing in a reductive atmosphere. Copper ions will replace alcaline ions, and a beautiful ruby colour will result in the surface plane..   "

The point is that one gets a unchangeable surface colour without the need for casing in a coloured layer of glass. The coloured layer is very thin, making it easy to cut, engrave or etch through, making clear patterns on the coloured object.

The photo below shows a vase, red-stained and then cut. The middle picture shows that the "painting" was not very exact. To the right a yellow-stained glass with intaglio décor.
stained glass objects

Lustre glass

A somewhat similar process is used to make "lustre" (iridescent) glass: here, too, there is an ion exchange in the surface layer.
In the literature we have found two possible methods: if the hot glass is subjected to vapours containing certain metallic salts (among them stannous (tin) chloride) while still hot, it will get an iridescent surface.
(An anecdote tells that "certain chemicals were thrown into the glory hole". Such glass was, and in fact still is, called "poison glass" in Finland, because the vapours were not very healthy... Similar anecdotes are told from Eda, from the beginningg of the 1900s.)

This method cannot, strictly, be called "cold", since the object has not been annealed.

The other method is a cold method, similar to the staining: paint on a paste, fire in "cold" temperatures.

In the USA such glass is often called "carnival glass", and is popular to collect. Read more about American lustre glass here (opens in new window).

A couple of pictures:
luster glass