This is starting to drive me a little nuts. I have a lens that separated. It's the eyepiece lens for one of my older cameras. I successfully completed the separation without damaging either element, and then cleaned off the cement with acetone. So now I have to lovely lenses, that show gorgeous fringing when I put them together. So next I bought some Canada balsam on the net. It came in solid form - big chunks of lovely amber coloured stuff. My first attempt was to clean everything carefully, then heat the lenses, with a little chunk of the Canada balsam on the concave surface. When that melted, I dropped the other lens on top, carefully aligned it, and left it to cool. I ended up with little air bubbles trapped between the elements. So I separated them again (much easier, as the cement hadn't properly set), cleaned it, and tried again. This time I noticed the Canada balsam bubbled a little as it melted. I figured the bubbling was water in the balsam boiling off. Once it had settled down, I placed the convex lens on. Still bubbles. I noticed they were appearing from nowhere while the lenses were still hot. So I kept them warm for a while in the hope that the bubbles (which I presume are water) worked their way out. But the longer I left it, the more yellow it went - clearly I'm burning the balsam somehow. I pulled them apart again and cleaned them. For try three, I dissolved a chunk of balsam in acetone. I put a drop on the concave surface, and dropped the other lens on top. It looked beautiful. So I left it be for a few hours. Sure enough, when I returned there were bubbles. So what am I doing wrong? Has anyone successfully done this? The UV curing lens cement from Edmund optics is looking more attractive all the time.