Short version:
NEVER EVER CLEAN YOUR PDP-10 PANEL !
The long story:
After the PDP-10 KI10 console panel arrived from shipment, it looked quite good, but also quite yellow.
Fresh from eBay
Of course it needed cleaning. The most critical part were the acryl glass plates with the colorful imprints.
Since I'm working with historic computer equipment for some years now, I startet the usual procedure:
I watered the panel plate in my bathtube, and added a good portion of usual household cleaner.
Cleaning plastic with water never has been a problem before. And with pleasure I watched my cleaning water turning brown:
But then things went terrible wrong:
After drying the panel, the transparent protective paint on the front panel turned gray and more opaque than before!
This was an irreversible chemical process. When put in water, the 40 year old paint cover turned transparent again, but in dry state it looks awful! This process can be repeated multiple times, but after the initial reaction the panel state does not change any more.
Dry panel plate
Wet panel plate
A macro photo reveals, that the paint is going cracky and developing a craquelure structure, like known from old oil paintings. And much much worser: On some places, the protective paint is ripping off the blue and white color behind when drying! For instance, see the damage on the "O" and "D" of the word "LOAD": the white color is going off, the black background is shining through.
Just awful !
On the photo the paint looks very loose, but it is quite hard to remove. I experiment a lot, but could not find a cleaning solvent to remove the corrupted paint while leaving the acryl glass intact.
So I started carefully scrabbing the paint off. Luckily in wet state, it get's a bit flexible and can easily be removed on most places. Best tool was a square rod made of beech wood. This took two weeks. I didn't dare to scrab it off over the symbol prints on the surface of the panel: I indeed damaged a few of these too!
All this restoration was carried out on the lower acryl plate only. The upper plate is still in its original state, I just cleaned the worst yellow dirt film off with very very few water and long long dry time in between. So the upper panel has it's orignal mat paint appearance, while the lower panel looks partly glossy, partly corroded:
So finally the panel looks quite stressed, but has survived my restoration attempts:
Other trouble
I was really depressed, and still I'am: Like an idiot I ruined this precious artifact by stupid cleaning, without at first testing my procedure at an invisible edge!
But perhaps it isn't my fault at all: apparently this paint is simply decomposing because of age.
In the Computer Museum Kiel these pictures were taken from another PDP-10 KI10. Here the machine in storage waiting for restoration:
Me again, fascinated again by a PDP-10 after 32 years
This closeup picture was made in August 2013 by Gabriele Sowada, the PDP-10 is on exhibit now:
Here the paint is not damaged by water contact, but has turned brittle and yellow on its own. If you touch the surface slightly, the particles are falling off.
This is bad news: these PDP-10s are fading away.
One more reason to visit them!