Canadian Balsam

[LewisM]

Trying to restore an OLD doublet - SMALL - that was joined by Canadian Balsam (given the age of the optics). The lenses were spun and press fit into the assembly and CANNOT be removed to clean.

Should Xylene, given enough time, work it's way in through the microscopic gaps etc eventually dissolve the old balsam, leaving me an airspaced doublet? This would be MUCH preferred than the unusably cloudy optics at the moment!!!

I tried heating the balsam over an incandescent bulb, but got it too hot and it browned (previously white crystalline), so literally cooked it. I have been soaking in isopropyl alcohol and acetone, and it IS between the lenses (as I can see a bubble, that moves when I turn the lens), but it seems to be VERY slowly dissolving it. Hoping xylene might accelerate things.

[allan gould]

so there is a gap between the doublet? Then drill two small holes oposite each other in the assembly an push th acetone isopropyl alcohol mix through it

[dannat (Daniel)]

You should be bale to loosen the balsam in a very slow oven,
You could also try xylene or acetone, be careful to mark both lens with a straight line so you know to line them back up easily, use pencil either heavy graphite or wax pencil

[LewisM]

Daniel,

I cannot get the lenses out of their housing (press fit, which would mean destroying the "tube" that surrounds them to get them out), so I have to rely on capillery action to draw it into the microscopic gaps.

Already heated it - took it too far and the balsam turned dark brown (cooked it!). I actually stopped it when it was clear, but the heat retention took it past. Damn it. So, dissolving the balsam to leave an airspaced doublet instead - best option at this point.

There is a small crack in the crown glass lens, so that is helping get the acetone/alcohol mixture in there too. The crack does NOT seem to hinder refraction at all, as it does not cleave at an angle.

[mercedes_sl1970]

Hi Lewis

I have been pondering this. I know you have already tried heating but could you try again at a lower temperature? Say, in a saucepan of water, slowly heating. I believe brass has a higher expansion rate than glass so you may be able to get the elements to release.

I had a similar problem with a WWII binocular eyepiece with which the balsam had crazed. The elements seemed fairly tightly bound in the eyepiece cell. I gently heated, well below boiling, and then they fell apart.

Could be worth a go?

Cheers

Andrew

PS I then re-cemented the elements with some UV curing goop.