U of S | Mailing List Archive | alt-photo-process-l | Re: Alt print on Glass?

Re: Alt print on Glass?

No, Jacek, that looks like carborundum in solid state for knife sharpening. You need carb powder, but where can you get that where you live, I don't know.

You take a pinch of the powder, add some oil or detergent to make a suspension and apply it to the glass. As Geoff says, you will need a tool. Nothing elaborate, I just use another glass plate, put the two together with the carb suspension in the middle, put all on a flat surface with some newspaper under it to avoid scratches on the bottom surface and work applying pressure on the upper plate with my hands. Unlike in telescope lenses building, the 'tool' will be usable also :-) This procedure is BTW good for making depolished focusing screens for large cameras. Keep the movement roughly circular, taking care to press not only in the middle but also on all the the borders. It will take some 10-15 minutes but you can wash the glass, leave it to dry, examine and if not good enough, start again.

Obviously, you don't need to clean the glass before depolishing. The ammonia-based detergent is to be used only if you want to use clear glass, which is factible even with gum, but more difficult.

As others have told you, fluorhydric acid is to be avoided unless you have lab experience. Or unless someone other does it for you.

The product mentioned by Paul Viapiano says explicitly "not recommended for large surfaces" so I don't know. What is a large surface, several square metres? You could give it a try if you can get it. But the carb method is simple enough and not that much work. Also non toxic but avoid breathing the carb powder, it could produce ... eh ... "carborundosis"? Ha ha.

Good luck
Tom Sobota
Madrid, Spain

Jacek Gonsalves wrote:
Hi Tom,

Thanks for the information. Can you elaborate more on carborundum? Is there a specific product I can get? Is it this by any chance?

Ammonium to clean glass, will try some Windex, that i'm sure has ammonia in it ! :)

Quoting Tom Sobota <tom@sobota.net>:


Printing on glass is not very difficult but the exact procedure depends
on the process.
I have made three-color gums on glass, but gum doesn't stick very well
on plain glass, so I first 'frosted' the glass surface with
carborundum. Well, actually a valve-polishing compound that has

I use carborundum because just 'sanding' the glass is, in my
experience,  very slow.

On the other hand, gelatin sticks to clean plain glass very well, so
any gelatin based process such as carbon works very well without the
need of any additional substrate. But the glass has to be VERY clean,
and that means at least some ammonia-based detergent. You could also
consult instructions for preparing glass for collodion. Glass is
notoriously difficult to clean well :-)

For maximum adherence of gelatin you could use some sodium silicate
substrate as used for collotype. However, for a quick test a reasonably
clean glass will do.

You don't need to brush the gelatin on the glass. Just flow it from a
flask, and help to spread it with a finger (or a glass rod). The
gelatin will dry to a nice transparent thin coat. Keep the glass warm
while spreading, and then cool it on a very level surface.

Tom Sobota
Madrid, Spain