Definitely the binder in the mica

We have learned a bit more about the condensed film we found on the glass inside the test cell. 

When we took that cell apart we found a good deal of condensate on the face of the end flange.  The flange would have been the coolest part of the cell, so that makes sense.  It also smelled like acrid, burnt electronic components.

We suspected the binder in the mica material or some residual oils from the coolant fluid during the machining process that may have soaked into the slightly porous mica.  Judging by the amount of residue, it makes the the residual fluid very unlikely.  To test it, though, we dry cut a small piece of the same mica, wrapped it with nichrome wire, and suspended it in a glass jar.  Our hypothesis was that if we heated the fresh mica it would off gas and the same residue would collect as a film on the glass.

Turns out that as we heated it, a grey smoke appeared in the jar.  We baked it like that for at least two hours before turning it off and letting it cool.

Close-up of the jar

Closer up of the heating element around the mica

When we opened the jar, we did find an oily film on the glass that had not been there before and it had a smell not too different from what was in the test cell.  While we did not notice any smoke in the test cell, we were not physically watching it for many of the hours that it was hottest.  Additionally, the test cell had no oxygen, so it may not have made a visible smoke.

Next we wondered if a different variety of mica that did not mention that type of binder would heat up without smoking.  Turns out it smoked at least as much, maybe more.  Reheating both samples of mica produced no more smoke, however.

Now that we have cleaned the cells out, our current plan is to assume that the material has been mostly baked out, and, since Celani used mica which probably had a similar binder, any residual, even if it were to settle on the hot wires wouldn't affect the wire performance.

An ideal solution from an engineering perspective would be to replace the mica with an entirely different ceramic known to be totally stable and inert at those temperatures, but since Celani used mica, that solution is not the best from a scientific replication point of view.  I am open to suggestions and input.