frit vs. enamels for colour
I understand that you are using bottles of which you do not know the characteristics. I was trying to gently point out that there may be compatibility problems. In my experience float glass and bottles are more likely to be compatible than fusing compatible glass. If you are selling these, you may need to do tests on how stable the results may be.
If you are going for colour, glass enamels may be a better, safer alternative. If you can spray glue into the bottles, you can spray the glass enamels also. The results will not have compatibility problems.