P3D Cloudy Heat Adsorbing Glass

["James R. Motley" <jmotley3d@xxxxxxxxxxxxx>]

Heat Adsorbing Glass (HAG) with a cloudy coating has been mentioned
several times in the thread started by Andrea regarding a TDC projector
(unknown model) melting a slide mount.  

One TDC 116 which I once acquired had HAG's which looked more whitish or
light gray than the usual light green color of HAG.  This coating looked
like a soap and high mineral water scum build-up on the sides of a bath
tub, but more difficult to remove.  I scraped off some of the whitish
film with a razor blade scraper but could not get it all off.  Also
several different solvents including paint remover did not remove the
film to get back to what I would expect was originally light green like
the usual HAG.

The blower motor had obviously been changed (the mounting surface had
been filed flat so that this motor would mount flat) and the squirrel
cage blower had a smaller diameter than those in my other 116 and 716. 
This projector (with 500 watt bulbs) did get hotter than the other two.

I speculated that this film may have been caused by excessive oiling of
the motor with some being blown onto the HAG and then being baked onto
the surface, perhaps something like a carbon build-up on valves in a car
engine or something spilling in the oven.  I do not recollect having
seen signs of oil coated on the condensing lenses or the housing, but
this was a year or so ago. 

Does anyone know for sure what this film is and what causes this to
happen???

Still puzzled.......Jim Motley


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