Can take up to a week. The line of solution moves slower when it gets past the discoloured layer.
The sticky remains of the balsam will still be on both internal faces when it loosens.
Canada Balsam is still available.
Think carefully about the reglueing sequence - don't try and fix the two joins in the three lens achromatic at the same time!
Did you know a drop of Wesson Oil between the elements can serve optically as a temporary substitute for re-cementing. Not very permanent, but I've got images taken with a petzval that front element was temped with wesson oil. Optically it seemed to work fine. Might have lasted for years, who knows.
Actone is fun stuff. About twenty years ago there was a paint mfg about three blocks
down the railroad track from here. One day every building around was rattled like crazy by a horrific blast. A tank car of acetone had become totally vaporized and they
never found the workman who was pumping it - apparently completely vaporized too -
but they did find his cigarette lighter laying intact right beside the railroad track.
Yeah -- and I found the paint on the bathroom vanity getting soft. Somehow, it was never her fault...Originally Posted by rdenney
In carbon printing one can use rubbing alcohol (isopropyl) or acetone for spirit sensitizing. I prefer acetone for several reasons -- a minor one being that the smell of rubbing alcohol reminds me of the many times I was sick as a kid and my mom would pour some on my back in attempts to lower my body temperature (often peaking at 104 to 105F).
Good luck in your lens project! Way to jump into it with both feet!
Vaughn
Nail polish remover is mostly acetone, but what is contained in nail polish itself would be illegal to sell in a paint store. It's basically a category of lacquer considered too dangerous for industrial use and is officially the very biggest source of toxic contamination in landfills! The cosmetics industry apparently has the influence money to fly under the radar. Lacquer solvents go right thru the skin into the bloodstream, unlike acetone which simply dries the skin out and causes it to itch. A known carcinogen too. That's why I substitute acetone for lacquer thinner whenever possible.
Might as well be sniffing glue. One of the local ambulance drivers was telling me about
how many women he had to ressucitate or defibrillate every month in nail parlors.
I did mark the glass in pencil - two places, about 120 degrees apart so I won't get confused later. Thanks for the cement links - is 3cc enough or do I need the 1 oz bottle (in which case I'll play with a couple of ugly bausch lenses I have).
I wish I had taken a photo of the cemented set before it went into the bath (in an old tomato sauce jar by the way) - I've never seen anything that ugly. I have a feeling it was separating and someone tried to reflow it.
The lens is an 8x10 Gundlach Rapid Rectigraph - 13", 20 1/2", 29", in a badly pitted worn brass barrel. It's probably not worth all this effort but its a good learning experience.
Dan
I have not worried about the relative rotation. 3cc is enough for many lenses, you only need 1 drop.
I tried using acetone, and then toluene, to "unglue" a badly separated doublet. After about a week and little progress (it was a 3" dia doublet), I changed tack and put the doublet in the oven. The balsam was soft enough in about 30 min to slide the elements apart easily. Clean up with acetone after that was a snap and I was ready to re-cement. I find this much easier than waiting for the slow diffusion of solvent into old balsam.
I use Canada balsam to re-cement since it is very forgiving, is easily removable, and has given me good results.
A few hints if you want to try this. Put the lens on something soft in the cold oven (I used a silicone potholder). Then heat up the oven with lens inside, this will allow the lens to slowly come up to temperature (I would not risk putting a room temp lens directly into a hot oven due to possible thermal shock). I used 275 deg F. Afer ~30 min, I grabbed the elements using newspaper ovenmitts, and was able to slide them apart. Then let them cool slowly on a small stack of newspaper. You will get a nice "pine forest" smell in your oven from the balsam, but I do prefer that to organic solvents. Of course, this method wont work for modern cemented lenses where balsam was not used.
cheers
Tim
Acetone is almost non-toxic (no. 1 for toxicity on the NFPA diamond); it's produced by the body during fasting and during pregnancy, when the added energy that metabolic pathway provides is needed). It is flammable as all get-out, however. Toluene is a ton more toxic and is a suspected carcinogen (the only reason it has any industrial uses is that it's still safer than benzene).
I did try decementing my first lens by soaking in xylene, but eventually gave up and used the oven. That worked superbly.
They are ill discoverers that think there is no land, when they can see nothing but sea.
-Francis Bacon
The thin back piece of glass is off (it did indeed just slip off on its own), wiped clean and sitting on the side already. The other two are moving along more slowly (I suspect most of the separation was with the thin one). If they come apart before the week is out, I'm going to try Jim's oil idea (how will olive oil work?) so I can use the lens at an event next weekend.
Dan
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