Do they look like that after only a few hours of use?
Powder..patch..ball FIRE!
It depends on the TEMPERATURE the unit was run at. The picture shows nothing more than water scale from heat, (lots of it). If they had used distilled water or even a commercial antifreeze as a transfer fluid the inside would probably be pristine.
The trouble with both of those options is tha you need a LOT of distilled water based on his tests, and if you are working on a test unit that will be opened and closed antifreeze is not fun or clean.