Hello fellow engravers. I've been using Thermark for about 10 years now. I did a sample piece of solid brass (C260 Cartridge Brass) about 5 years ago and then put it outside in the weather to see how it would do. After the five years I decided to clean one portion of the brass with a vinegar, salt and flour solution. Basically you just apply it, let it set for and hour then rinse off. Well it did a good job as you can see from the photo attached but the only issue is the Thermark came off as well. When I put it out there 5 years ago the Thermark was bonded. I believe it bonded because I used a metal polish (Mothers) to polish it afterwards. Can you guys take a look and give me your feedback on what you think might have caused the Thermark to come off?
Thank you for any feedback.