Ground Glass differencesgreenspun.com : LUSENET : Large format photography : One Thread
Am making a few new 'ground glass' pieces for my various cameras. Anyone know what differences you get from acid etching as compared to sand blasting? I know with sand I can get coarse to fine sand & even finer with aluminum oxide, as well as very even over the glass. I have heard sand blasting is more coarse but brighter than acid etched. Any truth to that? Or, if so how about acid etched with a light sandblasting in the corner areas? Then, standard 'float glass' as compared to higher quality glass? I am thinking of trying the water white Anti Reflection (clear, not non-glare) glass, etching or blasting the non coated side. Will this result in a brighter image or finer focus? If anyone knows, I would be interested in your experience as well as helping to avoid pitfalls.
-- Dan Smith (firstname.lastname@example.org), March 10, 2002
I'm not sure about the 'water white' glass, but I have heard that acid etching on standard clear window glass wlll lead to unevenness. This was verified by a fellow as a glass shop I was talking to when I mentioned I needed a 'ground glass'.
I had moderate success with taking untinted window glass and grinding it with value grinding compound. It worked ok, but I ended up getting a hot spot in the middle of the glass. It was very difficult seeing anything in the corners.
I ended up getting Toyo field that has a nice fresnel in it. It's very bright, and quite even.
You might want to look at aquiring a ground glass one from a place such as Edmund Scientific (edsci.com). From the description on their web site, they do a dual-pass 220 grit sandblast. Sizing seems pretty limited, however, so maybe not so useful for you.
Hope that helps.
-- Ken Miller (email@example.com), March 10, 2002.
I've made a variety of pieces of ground glass for cameras and instruments using common float glass, old glass plates, and whatever else could be had surplus or cheap. Use silicon carbide grease mix (Clover Compound) from any machine shop supply company (Travers Tool, MSC, etc.). The problem with all ground glass (and no fresnel) is balancing brightness, focusing ability, and hot spot. Too fine and you tend to see through it. Too coarse and it's hard to see detail and focus. I use 320 to 600 grit, depending on application, though I like 'em finer rather than coarser. I've etched some glass with HF acid and wasn't very impressed, though maybe others have some secret technique. The surface quality was peculiar. I've also done fine sandblasting and it's hard to get things even. Best method is to grind using a small piece of glass on the large piece, say 1" x 1" or a bit less- grind the edges with a stone so you don't cut yourself!
-- Conrad Hoffman (firstname.lastname@example.org), March 11, 2002.
I spent a good part of last week reading about this. It seems that there's a good reason it's called a "ground" glass - grinding gives the best finish. Etching with acid produces a fine finish, but is very difficult to get an even finish. If you want acid etched, you're better off buying a piece from a glass supplier (look for stained glass suppliers). Sandblasting is also difficult to control. Grinding provides the best chance for success. Coarse grit gives you a rough surface that is brighter but "lower resolution".
Check this link for some hints: http://people.smu.edu/rmonagha/mf/glass.html
I was ready to buy some glass and grinding compound but then decided I should be out shooting instead... Maybe the next rainy day I'll make a backup gg.
-- Dave Mueller (email@example.com), March 11, 2002.
I used a glass bead blaster, and found that it was very easy to over do. I wasn't happy with the results at all, but you could focus on it. I suspect grinding is the way to go, but I haven't tried that.
-- Neal Shields (firstname.lastname@example.org), March 11, 2002.
I have made several up to 5X7 using dry powder carborundom from a lapidary supply. #400 to #600 grit range is what works best, I'm using 500. There are specific directions on how to do this somewhere on the web. Jon Grepstad's site used to have it: (now it looks like you have to buy the book) It is easy to get an even texture over the entire glass. Start with a larger glass on bottom, and the GG-to-be on top. Make sure the glass and work area is very clean. Set the bottom glass on a smooth flat surface. Sprinkle the Carborundum on the glass (rounded teaspoon will do a 5X7.) Spray some water on it to form a runny paste. Work the GG piece on top in circles. Work the top piece down on the paste until it forms a very thin layer between the 2 glass surfaces. About 15-20 minutes of random grinding, and rinse it well with water, check it. If the corners or center needs a little more, work it more until the entire surface is even. Change the position of your hand on the glass to even out the pressure, working the corners and the center. You can't 'overwork' part of it: when it's done, it will be extremely even. Get several different grits if you like and see what works best for your taste. I have found this method very easy, safe, and makes an excellent and consistent GG. I have no urge to 'upgrade' them.
-- Gary Frost (email@example.com), March 11, 2002.