Having bought a rather beaten up Graflex Speed Graphic, I discovered that the rubber sealing material on the silk was perishing. Instead of having a light-proof barrier, there was a mass of pinholes. It looked OK until you put a very bright light behind it.
I became suspicious of the shutter when I failed to get good results from a 135mm Rodenstock Rogonar lens. The Tessar I used worked well but it had its own shutter. So I checked the focal plane shutter and found the rubber was perishing.
The Web told me that this was not an easy task. Most suggested you would have to pay for a replacement. That was not on.
While playing with ways to deal with the perishing rubber, I tried a number of possible solvents. Acetone (proper stuff not substitute nail polish remove) proved be able to dissolve, at some level, the rubber coating. I thought it was also spreading the softened coating to produce a new seal but that did not last.
I took much of the coating off a couple of sections but was not brave enough to go the whole hog.
I had been using white PVC glue mixed with a blacking agent to help with the re-sealing of bellows. This had worked reasonably well. But it was too thick to use as-is on the shutter.
The I remembered that when I had been using ordinary plastic house paint on plastic surfaces, the paint usually came off as a flexible sheet. The shutter was no good as is so I had nothing to lose. I began by testing PVC and glue on some fine weave cotton. It was not as fine as the shutter silk but would be an indicator. The PVC was too rigid but plastic house paint appeared to be more flexible.
I mixed a high quality vynil mat house paint at about 10 parts paint to about 2-3 parts water (including pigment). Exactly how the mix would work across manufacturers and across countries is a problem. The thickness of the mixture was such that when I dipped a wooden toothpick in about 4cm and then withdrew it, the paint did not drip of the point until a good blob of paint had formed.
I coated the film side of one curtain and checked it after it dried. And it seemed to work. But wouldn’t it be easier to pull the shutter unit apart and do it then?
Looking at the way the cloth expanded with the application of the paint and then contracted nicely as it dried, I decided that doing in situ might help maintain the integrity of the shutter cloth.
I took the back off so that I could go to the edges of the cloth - I was doing all curtains on the film side not the shutter side.
I paint a whole visible curtain surface and let it dry for an hour or so or until it is touch dry - at about 18-20C.
Then I run the shutter a few times, rolling and unrolling that curtain.
I check for holes and repaint sections, repeating the drying and testing process.
My rationale is that I want to flex the paint. Someone might be able to give a best point for this that is technically sound.
Then I move the shutter until it uncovers the a section of the same curtain that was not done - remember that the whole curtain is running and holes on end sections will cause problems. I repeat the above process.
To date it is working. But it is possible that the paint will gradually break up.
What is also the case is that those curtains from which I partly dissolved the rubber needed more attention. I have put a coat on the lens side of the cloth with these.
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