"Turns"

"Turns" is a term most frequently used with reference to electroless nickel ⇦ huh? plating baths. What happens with these baths in use is that the nickel content plates out and at the same time the hypophosphite reducing agent deteriorates to orthophosphites which are not removable and eventually require replacement of the bath.

Usually it is possible to replace the nickel which has been consumed, and keep the process going, but only up to the point where the bath must be dumped and replaced due to orthophosphite build-up. If the nickel content can be replaced 3 times before the orthophosphite prevents further use it would be called a "3 turns bath". If the nickel content can be replaced 10 times before the bath becomes unusable it would be called a "10 turns bath".

Suppliers work hard to offer processes with as many turns as possible.