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.
Jacek Gonsalves wrote: