WHITE AND BLACK 
White as snow, red as blood, black as ebony- these are the colors of beauty in fairytales. Milky 
white skin is lauded by the poets; the white of snow and milk - is it the same as the color of ala- 
baster, the white of the opal? 
The white of porcelain has many colors: a delicate gray, yellow or blue caused by raw materials, 
the mixture of the batch, glazes, the degree of heat in the furnace. dass gives the white an addi 
tional dimension, that of transparency. Subtle differentiations in white occur: translucent alabas- 
ter-like hues, enamel white opaque, changing itself in the changing light; bluish opalescent, play- 
ing with yellow; there is a hint of color in every white. For that reason, it also bears many names: 
milk glass, bone glass, opal glass, rice glass, alabaster glass, cryolite glass, spar glass. Difficult to 
describe in words, almost impossible to pin down in terminology, they enter speech through their 
optic effects (alabaster glass), or their raw materials (bone glass, spat glass, cryolite glass). 
“The purest white and the deepest black are the two poles, between which the actual colors, yel 
low, red and blue and their various mixtures, lie. White is a delicate color; the barest hint of an- 
other color cancels it.” (Gräbner, 1837, p. 6). 
In works on glass technology, “white” glass is often used in a double sense: on the one hand as 
actual white (color glass), on the other hand as “white hollow glass” in the sense of crystal clear, 
colorless (de-colored) glass, whose brilliance is enhanced by polishing and cutting. To make the 
confusion even greater, “semi-white” glass is to be regarded as a preliminary stage towards co 
lorless glass. One saw "... the greatest beauty in glass in its most perfect transparency and total 
lack of color. . .” (Scholz, 1820, p. 143). 
Every interpretation of Contemporary literature must be carefully examined as to which meaning 
the adjective “white” refers to - colorless or in fact white glass. The equation of milk and bone 
glass by some authors contradicts others. Sometimes the term, “milk glass" is meant to be re 
garded as a heading for a group of glasses, sometimes there is a differentiation between milk and 
bone glass. When technical terms such as devitrification or opacifying are used alongside the 
term “coloring" in a discussion of the manufacturing process for white glass, a layman’s interest 
is frequently overtaxed. It may be a help in understanding the problematics to go into a historical 
definition of terms and technologies. 
If we take transparency as a measure of degree, we can differentiate between more or less tran 
slucent and completely opaque glass. Opaque white glass (white enamel glass) is made by using 
tin oxide. It is especially suited for overlaying (casing) and is only translucent when it is ground 
very thin. The opacity in translucent glass results from devitrification or the addition of opacifying 
substances such as bone ash (= phosphoric lime). At the beginning of the 19th Century, one dif- 
ferentiated between “opal-colored glass” and “non-transparent white glass.” The former was 
glass decolored by manganese oxide or arsenic with the addition of “phosphoric calcareous earth 
(calcined bones, preferably of sheep).” The “non-transparent white glass” was glass that was de 
colored with manganese oxide or arsenic with the addition of tin oxide (Loysel, 1802, p. 267). 
In Benrath we find (Benrath, 1875, p. 275): 
1) Glass, whose opacity results from regulär devitrification 
2) that to which tin oxide or phosphoric lime has been added as an opacifying agent and 
3) milk glass rieh in aluminum oxide, which has been appearing as cryolite glass for a number of 
years. 
Bruno Bücher sets “milk glass,” “bone glass" and “opal glass” apart in the following manner: 
Boneglass, by way of the addition of bone ash, white colored, not transparent but only tran 
slucent glass, which shows a brownish or reddish tint when held against the light, and in this way 
differs from milk glass. 
M i I k g I a s s , ital. latticinio, through the addition of tin oxide, a cloudy whitish colored, translu 
cent glass is made, which shows no other color when held against the light. Cf. Beinglass. 
O p a I g I a s s , glass which, through the addition of bone ash or a bit of silver Chloride, attains a 
milky color and the sheen of opal. (Bücher, 1883, pp. 26, 256, 276). 
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