Antique ground glass emulsion

[gorbas]

A friend of mine is restoring 30x40cm (~12x16") camera from around 1900. He is very experienced LF camera builder.
On this camera he found unusually bright (even in corners) ground glass with super fine texture, yellowish in colour. Glass already had some clear spots but when he tried to clean it with wet cloth, ground glass texture started to melt/dissolve and become transparent. He did try to replicate it with emulsions made of eggs white, shellac and gelatine but he can't replicate fine texture of original one. Does anybody knows what secret ancient emulsion was applied to this ground glass? Personally I never heard of any other kind of ground glass with emulsion applied on it.
Thank you in advance!

[Erik Larsen]

Wax perhaps?

[Jac@stafford.net]

Is he sure the glass is original? Some people use hair spray on plain glass for a bright screen.

[DrTang]

Is he sure the glass is original? Some people use hair spray on plain glass for a bright screen.

Hahhaha - I had a 7x17 once I used wax paper on

[gorbas]

Thank you guys!
Emulsion start melting after being touched with water, so I don't think is wax based emulsion. Also I haven't seen it in person. So far I think it's original ground glass. It had bunch of pencil lines marked for different formats

[Michael E]

My 30x40cm camera has a "ground" glass made in the same manner - clear glass with a matt coating. Looks original. I have no idea what was used in the process, sorry.

[LabRat]

Could be something like waterglass mixed in gelatine??? Check some of the old 19th century photo technical books/guides, as they often had different processes described for other photo related processes... (After the sections with the formulas sections, usually under "darkroom aids") Old Photo Lab Indexes had this section...)

Steve K

[Randy]

I have a book on building large format cameras and it gives instructions on using 1% milk, coating the sheet of glass with it and letting dry. I haven't tried it but that could be what was used. I don't know if this is a more modern DIY technique or an actual practice from the past.

[Jac@stafford.net]

I have a book on building large format cameras and it gives instructions on using 1% milk, coating the sheet of glass with it and letting dry.

Skim milk works as well. The additive that makes it work is Titanium Dioxide which makes skim or 1% white. Otherwise, the 'milk' is a watery blue. Titanium Dioxide is probably the most widely used white pigment in products from food to paints. But before 1900 milk was whole. No additives. In fact, commercial pasteurization wasn't introduced until about 1890.

Whole milk dried on glass just makes a stinking mess.

[gorbas]

Thank you all for the help! I will try to keep you posted of the final solution used.