A micro riddle

[Pau]

Very flat subject...do you know what is this? (well, I'm not sure...)
The colors are due to interference.

Crop to better show details

Dark field with a Leitz Plan Apo 4X 0.14, Zeiss WL, afocal 6.4X on Canon 7D APSC sensor, 16 frames stack.

[Scarodactyl]

Delam perhaps?

[Pau]

More images, now taken with a 10 Pl Fluotar and a green interference filter to avoid chromatism. Single shots

[Pau]

Delam perhaps?

This is one of the main suspicious, the thing is inside an optical element. The aspect suggests something biological, but maybe only because the morphology

[Pau]

On location:

The thing is inside a Zeiss Jena 1/4 wave plate microscope compensator. Canon 50 mm f2.5 at f8

Crop to show the whole monster

[Scarodactyl]

Note I regonize the symptom but didn't speculate on the cause. I have seen unambiguous crystallization between elements and (of course) unambiguous mold, and this kind of stuff too but didn't get a better look.
My bet is crystallization on this though, too strictly dentritic even with the weird little isolated zone of growth.

[Pau]

To me this doesn't fit with crystals, no birefringence under crossed polars (although the own properties of the substrate could affect it) and no straight lines.
Any reference, please?

[Scarodactyl]

Probably hard to be completely sure of birefringence when it's embedded in a quarter wave plate, right? I've watched crystals grow this way, dendritic growth isn't restricted to straight lines. They'd start out sharper but quickly smooth to get a lower surface area to volume ratio. Or it could be mold of course, they'd be driven into a similar shape by similar competition for locally depleted resources.

[Bob-O-Rama]

That is gorgeous and the comb like structure is very much unexpected. I wonder if this is growing at a fast enough rate you could observe it with a time lapse.

[Pau]

Examined for UV autofluorescence there is no emission (many fungi are fluorescent).
The mystery remains although fungus growing in the cement between glass and quartz elements is still my main candidate, despite I agree with Scarodactyl in that this doesn't closely resemble typical lens fungus.

Any other thoughts?

That is gorgeous and the comb like structure is very much unexpected. I wonder if this is growing at a fast enough rate you could observe it with a time lapse.

Thanks, Bob
I now imagine the monster growing fast over all my optics and even my studio walls and furniture...a terror movie!
No, whatever is it, it's growing very slowly, likely it has taken several years from when I bought it apparently good and now

[PeteM]

Lens fungus can also look like this. For example: https://www.truetex.com/lens_fungus.htm

The orderly progression of this and its limitation to one semi-circular area near the edge of the wave plate might mean a combination of delamination with fungus growing in the slight opening between glass elements??

It IS beautiful, but probably best kept dry and away from your other lenses.

A microbiology professor friend likes to point out that fungi are genetically quite close to we humans. Perhaps offer it on Ebay as a one of a kind miniature artwork, delicately and laboriously (years!) carved in glass, by what just might be a sentient extra-terrestrial beings.*



* It seems that fungal spores might survive a space transit.