Antique ground glass

[gorbas]

A friend of mine is trying to restore old 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 eggs white, shellac and gelatine but he can't replicate fine texture of it. Does anybody knows what secret ancient emulsion was applied to this ground glass?
Thank you in advance!

 

[tedr1]

I haven't encountered that kind of screen but this is a guess, there is a method of adding a wax layer to a glass screen, I think it was used by a Dutch company named Bosscreen.

 

[AgX]

Aside of guessing on that kind of surface treatment on that pane, the laws of physics remain: the brighter the image becomes, the more directional it will become too.

 

[Kawaiithulhu]

I haven't encountered that kind of screen but this is a guess, there is a method of adding a wax layer to a glass screen, I think it was used by a Dutch company named Bosscreen.

With Boss it was a layer of wax between two glass sheets. Here it was just wax rubbed into the surface of the ground glass. It works in kind of the same way that oiling a piece of parchment will let more light through. Shellac was a good guess, I see it come up in one or two queries of DIY ground glass tricks and solutions.

 

[BrianShaw]

I don't know if this will help or not, but from a 1903 photography book: obtain a piece of glass exactly the same size as the original screen. Take some negative varnish, thin with menthylated spirit and varnish the glass in a manner precisely similar to that of varnishing a negative. Let cool then rub with s finger until it loosens in the form of s whitish powder. Carefully brush away the powder and screen is complete.

Personally... I'd not be so authentic and replace it with a modern ground glass.

 

[John Koehrer]

Would a light dusting of matte clear coat work?

 

[gone]

Yes, GG and a cheap DIY fresnel should be plenty bright enough.