How I did it: new balsam for a sick RR

Just an update!

My first bottle of Canada Balsam no longer pours, but is still usable by geting a piece on the end of a glass rod, or similar, and letting it contact melt off onto the warm glass.

This time I have done an older lens - the Ross Actinic doublet - the Ordinary Angle version. This is one of the attempts in the battle for the "RR" design!

About half the balsam layer was discolored yellow. It took the usual 7 days of Xylol soaking. Once again, the balsam had left a Chalk looking deposit over the whole of the concave surface. Again this was removable quite easily with water based solvents.

This was very different type of lens mounting. The photo shows the cell with half the blacking enamel in place. The cemented lens is much smaller than the mounted lens - which is part covered with black paint or shows its mat rear surface.
This is good in respect of escaping the trouble with fiddling with the brass but means that fixing the cleaning lens in the balsam hardening process is more tricky. It also means that a total balsam failure would mean the demise of the lens as it would fall off.
I have just painted one side of the lens to show the GG surface of the fixed lens. The other side is fully polished. I suppose this use of "oversized" lenses is the price you have to pay for standardisation of mounts/barrels. This is the 4x5" size.

Are there companies out there that will do a re-cement for a fee??? I have a darlot with a seperation in the front element, while not overly bad for wet plate type work, I would like to make it 100% again. More importantly, seperating and recementing the lenses so that the original Darlot pencil marking on the edge is not disturbed would be ideal.... Any ideas?

I think the original Darlot marks would be untouched by traditional Canada Balsam. I'll do some experiments with pencil marks next time I split an achromat.
In the soaking/delamination you can get them to restrict the amount of fluid in the container so it only reaches the line of cement. Or/And you could use a water-based clear varnish on the sides and let it dry out before the separation.
I believe the traditional Grimes organisation does (sub-contracts?) balsam work.
I hear that the UK contact for Balsam, Balham Optics, has ceased to exist. Perhaps they will re-emerge as the Bellows company in Birmingham did with a employee buy out.

I have just "forged" the usual Darlot pencil marks on the side of an achromat. It is not removed by flowing xylol and required quite a lot of rubbing with a xylol soaked cloth to remove all traces. Liquid Canada Balsam did not disturb or lift the pencil marks.

Thanks Steven

This is an update - mostly because some people have sent PMs recently about feasibility of doing it themselves.

1. Aging of Canada Balsam in small bottles.

I have 2 small bottles bought in 2009.
I have used about half of 1 bottle and have just started the 2nd bottle yesterday. The 3 year balsam in the full bottle is still almost without colour but the 1/2 full bottle does now have a noticable yellow tint. This, I suppose, is the result of oxidation. I think it is perfectly useable however.

2. Preheating and baking.

I now limit the prewarming to around 65 grad C. I also preheat the glass rod used to "fish-up" balsam from the container. I restrict the "baking" to a couple of hours at the same temperature (65C).

3. Applying the balsam to the concave surface.

I use a glass rod to apply the balsam at the centre of the concave lens. Reason - attempts at pouring, both mess up the balsam glass seal and (can) create tiny air bubbles which are a problem.

4. Even clear separation can have insoluble deposits on surfaces. Remove with finger nail.

5. Expect the solvent to loosen the edge black paint!

6. Don't expect the two (or more pieces) to fall away from each other. When I can see the liquid phase has nearly reached the centre, I dry the lens and push across. If there is some displacement, I begin to rotate carefully. Repeat soak if no success!

Could a Moderator move this to the DIY section?

Will be trying with a 4 glass lens in the next week (Zeiss Protar series VIIa).

Quote:

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Originally Posted by Steven Tribe

I am not sure how easily methylene chloride (CH2Cl2) is available anymore. It used to be the active component in really effective paint removers. Perhaps "wicked" was an understatement. The commericial product was rather gel like so there was time enough to place a dollop in a glass container (not plastic here) close the lid and retreat quickly inside.

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Methylene chloride is the Weld-On #3 solvent for use in sticking acrylic together. Readily available hobby item.

Rick "moved at the request of the OP" Denney

Quote:

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Originally Posted by twalsh341

Methylene chloride is the Weld-On #3 solvent for use in sticking acrylic together. Readily available hobby item.

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Pure methylene chloride seems to be unavailable at the retail level, chem supply places might have it,
the Weld-On #3 has an added components to it, I have a bottle of Methylene Chloride from yore that I recently
came across and the odor doesn't have a pungency to it that Weld On has.
You don't want to damage the glass !

I have had luck separating elements with Acetone. I recemented a couple of Computar DL enlarging lenses a couple of years ago. They probably had some modern type of cement, but they are prone to separation. The Acetone worked in about a day turning the cement cloudy. I recemented them with Balsam in the oven with small machinist's steel V-blocks. Afterwards I used a Sakura pigment brush/pen to darken the edges which worked quite well. I am pretty sure I used this thread as reference, so thanks Steven.