How I did it: new balsam for a sick RR

[Steven Tribe]

This is a update.
I have done three more balsam jobs since the last posting.
A few more tips - based on these extra experiences.

Temperature/Times:
The prewarming of the lenses before applying a drop of balsam works well at around 60 degrees C - there is no need to heat it up for long.

I have found that "baking" at around 75 degress C is enough to stiffen the balsam after assembly. An hour is sufficient.

I have found that using acetone for removing excess balsam and finger marks is the best solvent on a piece of absorbent papir. The solvent remains in the paper and will not seep down to the balsam layer.

Do not bake too long with excess balsam on the lens. I forgot a lens pair for 3 hours and the excess balsam formed a layer which was no longer soluble in organic solvents.

I enclose a before and after shot of a landscape meniscus. Received to-day and repaired to-day ( a very wet day outside - like October) ! This was a "quicky" as the lens had a screw retaining mount and the separation of the two halves was already complete.

[SAShruby]

Canada Balsam Source I

Canada Balsam Source II

Canada Balsam Source III

[c.d.ewen]

Canada Balsam Source IV

Can't link directly; you must search for "Canada Balsam"

Charley

[CP Goerz]

A hearty pat on the back for the posts Steve, I've had a bottle of balsam in my drawer for ages...maybe I'll use it now :-)

[Steven Tribe]

Thanks Andrew!
None of the purchases from you needed any treatment though. The good thing about balsam is that one has more time for checking allignment, a mistake can be easily rectified and excess balsam on the edge provides an excellent "fitting" medium in the brass mount.

[Sethasaurus]

Thanks for sharing your experience, Steven.
I have a lens I want to re-cement and I found this info which will also be useful to people:
http://www.skgrimes.com/popsci/index.htm
http://www.skgrimes.com/popsci/pops/index.htm
http://www.skgrimes.com/popsci/burnish/index.htm

[Steven Tribe]

I think some of these Grimes' notes are new.
Unfortunately, we don't all have a large lathe in the garage! The only problems I have with his description are
- heating as a means of separation. I have seen many cases of completely dried out balsam that wouldn't soften.
- heating lens + balsam in place. Balsam develops a "skin" on the top surface very quickly which will prevent satisfactory adhesion to the "top" lens. I think separately heated lenses, addition of balsam, placing the top lens on top quickly, obtaining the right fit, binding together, followed by gentle heating, is the best method.

I have removed the burnishing holding the lens with an ordinary file. It requires discipline and I always protect the glass surface with tape. It is not necessary to file through the complete thickness before it can be "broken off".

[desertrat]

Kremer Pigmente in Germany sells canada balsam:

http://kremer-pigmente.de/shopint/in...&product=62110

They also sell all kinds of pigments, resins, varnishes, adhesives, just about anything an artist or musical instrument maker might want. Some of the other resins might be good for making things like retouching varnish from old recipes.

In the US, Wood Finishing Enterprises sells similar items:

http://www.woodfinishingenterprises.com/varnish.html

I haven't bought anything from either of these companies, but might for future projects.

That's a great article on recementing lenses. I have one that needs to be done.

[Steven Tribe]

Interesting products! And in Euroland too.

I am rapidly coming to the conclusion that as many as 1/2 of our 19th C objectives could do with a renewal of the canada balsam. When I compare the redone cells with an original cell (which seemed OK), there is a very marked difference in the general clarity of the two! Even those without discoloured edges or crystalline "flakes".

[desertrat]

I like the idea of using balsam to recement old lenses. Modern adhesives have certain advantages, but the big advantage of balsam is that it can be done over again if it doesn't turn out right the first time. I need a process that's reversible, because very likely I won't get it right the first time.