Quoted from jfh:
Ok. If you were running Stern, how would you address this situation and what would your criteria be for playfield replacement?
I would keep it as simple as this:
1. I might apply a sanding sealer (a really thinned lacquer) to the raw wood before painting to fill in the pores and make the underlying surface harder. I would use a duromoter to test the hardness of the wood before continuing and see if it was within a predetermined specification.
2. Make sure my supplier is using a finishing process that has the correct amount of time needed to have an effective dry/cure process.
3. Use a durometer to test the final coating. This could be as simple as a pencil scratch test (a set of calibrated pencils that mark paint coatings and produce a quantifiable hardness rating). If the coating was too soft (for whatever reason, including trapped solvents), it would objectively fail to be within the correct specifications and be, per se, a defective coating.
4. Use an ultrasonic thickness tester to test the thickness of the final coating. If the mils fall outside of a predetermined range, I'd fail it.
But I'm not Stern and won't pretend I'm more of an expert than they are on the subject. I also don't know if they are already doing this or perhaps something even more rigorous. I also recognize that they, as a large manufacturer, have a lot of additional factors to consider.
So from a consumer perspective, I suppose if I felt so inclined, I would simply use a durometer designed for paint to measure the finish hardness and compare it against other clear coats from other machines as well as the general specifications from several lacquer companies to see if it is either in spec or out of spec. If it fails, I would consider it defective as a matter of fact and leave Stern's response to its costumers to their own desires.