Question about markings/strange glare

[codex0]

This is a Voigtlander 42cm heliar that I have - the glass is fairly clean, but I notice this strange pattern when looking at the front element in the glare of a light. It doesn't appear to be on the front surface - is this a condition of the cement between the front elements?

edit: fixed image size
http://codexphoto.com/temp/heliar/detail_of_glare_small.jpg

[Steve Hamley]

Hard to say without seeing the lens "in person", but it's likely oxidation of the glass, or "bloom". It doesn't look like separation or fungus. If you can unscrew the cells, you could clean the exterior surfaces with lens cleaner ans see if that helps. Sometimes there's some internal buildup on surfaces over the centuries.

Cheers, Steve

[Steven Tribe]

I beg to differ with Steve!
Blooming is usually more asymmetric/colouful than this. In the early Heliar design the front lens (concave/convex) is much thinner than the lens behind it. So it will look close to the front surface.
Strange things happen in Canada Balsam. The regular size of the circles suggest an intact balsam layer (same thickness between the surfaces) but that some crystalisation of one of the components of the balsam has taken place. As likely as not, the process may now be complete and there will be no further deterioration.