View Full Version : How to separate modern UV-cured plasmats for recementing?

John Schneider
20-Feb-2012, 22:08
I've done a few classic lenses made using Canadian balsam cement, whereby I was able to separate the lens elements in an oven, wipe off the soft balsam, and clean the surfaces with xylene. Recementing was with UV-cured cement.

Now I have a modern plasmat-design lens (probably 1980s) that I need to recement (I feel that the lens is worth the work). What do you suggest to loosen the bond between the two cemented elements? I have access to the typical solvents (acetone, MEK, toluene, xylene, acetonitrile, THF, etc.) and a nice programmable industrial oven (thanks, NSF!).

Kevin Crisp
20-Feb-2012, 22:41
A recent post suggested boiling in water would do it. I have not tried that.

When I use a modern UV cure solvent and then decide to redo the surface I just did, I find that soaking in MEK works well. You just have to be patient as it can take a week. If it isn't working (shown by a cloudy ring progressing inward) you'll know in a couple days.

Saunders also makes a solvent for this, you are supposed to heat it on a laboratory hot plate (i.e., no exposed orange glowing coil) and it is quite flammable.

Steven Tribe
21-Feb-2012, 14:10
One vote for methylene chloride (paint stripper). Stay away from heat sources and work outside.

I have never attempted this with a modern lens as mounting has become extremely complex, special tools for assembly and collimation are necessary and the collimation process itself.

Paul Fitzgerald
21-Feb-2012, 19:54
Another vote for methylene cloride, so does Norland Optical Adhesives.

Norland #61 UV adhesive (http://www.norlandprod.com/adhesives/NOA%2061.html)

22-Feb-2012, 07:30
If you figure out a good way to do that (that doesn't cost more that a replacement lens) please post your results. I spend a week or so searching threads and came to the conclusion de-cementing modern lenses was not feasible with the tools in my workshop (http://www.largeformatphotography.info/forum/showthread.php?85695-The-BEST-way-to-solve-lens-separation).

Steven Tribe
22-Feb-2012, 13:08
I hadn't seen the recent thread from ic-racer but agree completely. But it must be remembered that many older designs are similar. That is, many balsam joins are well away from mounting. These can be at edges or even with a "fried egg" sort of design, where the correct radius has ground/polished out in the center of a larger lens and the outer ground glass covered with masking black paint.

22-Feb-2012, 14:56

As hard as it is to believe there are some cements that will not de-bond with anything. When you do a balsam lens DO NOT USE HEAT. Just stick it in a tupperware jar of acetone and let it sit. be patient it will soften and come apart. You will have no thermo shock. Summers (link above) needs a lab style hot plate with thermostat. DO IT OUTSIDE!!!! The fumes are flamable!!!! After you hear the bond break turn off the heat and let it cool to ambient temp before you touch the lens.