"Before I leave the subject of broken ground glasses I found that a very adequate emergency replacement could be made. Just go to a local hardware store and have a glass cut to the proper size. Tape Scotch brand Magic tape to one surface of the glass. The tape is frosted and will work in a pinch as the ground surface. The image is serviceable but has a streaky nature to it. Make sure that the tape runs all the way to the edge so that the ”ground“ surface is at the proper plane. "
As Al pointed out Dick Dokas had published the emergency use of tape on glass in PT magazine in the 90's. A few years ago I was with some friends in Bluff photographing. One of us had a light weight camera, and took his hands off the tripod for a moment to get something out of his pack - and a breeze blew up at that moment to catch his camera and take it down. The only thing broken was - you guessed it - the ground glass. He was able to get a piece of glass cut to the right size, and was going to try and grind it. I recalled Dick's article and he was able to photograph the rest of the trip.
This effect is well known the finer the grind on a GG the brighter it is but the more there is a hot spot in the centre.
As a result, some will wax ( or laquer or nail polis) a spot in the centre (or any other area you wish) and have a bright easy to focus area and with a coarser grind +/- a fresnel have an area of easy composition. the scotch tape works like this.
After trying the tape I thought I'd try some Vaseline on the lens side of the gg...wow! That alone has made the gg significantly finer and brighter and easier to focus!
Your first response viewing through a little strip of tape was pretty close to mine. But Vaseline? Surely, you jest. If not, wouldn't the Vaseline "outgass" some petroleum product that might accumulate on the inside of the camera and the back of the lens? Maybe it doesn't get hot enough in Scotland.
Wonder what a little spray acrylic would do.
Just to mention, it has been about 6 years since I repaired that broken GG on the 8x10. I never used a fresnel with that camera. But I've since forgotten all the experimenting I did and checking today my 4x5 Graphic View, sure enough, I'd put tape strips on the GG's frosted side and replaced the fresnel lens--the tape sandwiched between. Works very well.
Copywork with exposures at F22 probably masks any slight change in the focal plane. The tape thickness is probably less than the normal variance of manually focusing the lens--especially if you are guessing some ideal focus point at a wide aperture. In the future, I'll take the advice to add tape of the same thickness right to the glass edge to shift the GG back in its frame.
Douglas, aye Vaseline! I rubbed in a spot of the stuff right up to the line of the tape, cleaned off the excess with tissue then had a look. The scotch tape area was brighter but the Vaseline area was still plenty bright. When I then removed the tape it left a sharp line clearly delineating the non treated gg side from the Vaseline treated side and again the difference was/is eye popping.
Focusing with the vaseline treated side of the gg is improved significantly!
The out gassing thing did cross my mind because theres always a lens folded up with the Tech....hmm?
OK... I just cleaned the Vaseline off the GG with a smidgen of soap and a polyester cloot, thats a cloth not a camels toe;-) then rubbed some butter onto the GG instead...works great!
Will butter attack my lenses or camera...? I'll end up frightened to leave the house!
I'll away and make some tea and butter the rest of the GG!
The things you get up to when the weathers grim and business has died on its arse!
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