What alternatives are there to ash forming oils and how compatible are they?

The alternatives to ash forming oils:
Formulating ashless oils involves selecting additives that contain no metal compounds. The challenge for ashless oils is therefore to provide a level of performance that is appropriate for whatever it is they are being used for, but without all the disadvantages of ash forming oils.
Preference is given to ashless oils in the following cases:

• Circulation oil used in a humid environment (paper machine, machine tool, rolling mill) 
• Biodegradable oil
• Food grade oil

Compatibility between ashless oil and ash forming oil
Two lubricants can be incompatible because of the base oils that they use, as well as because of their additive types.
Several laboratory compatibility tests between ashless mineral oils and ash forming mineral oils have resulted in the formation of deposits. This would suggest that the two additives are often incompatible.
Consequently, should there be any doubt about the compatibility of an ash forming oil with an ashless oil, a specific laboratory test will need to be carried out.