I typically just mix the mineral spirits right into the main container. I hope that helps
Rhonda

There’s 2 things I would do. 1 look at using an oil base paint from Rustoleum, I’ve done it in my bathroom on countertops and it’s worked great. But since it’s backsplash it’s really not going to be touched you could just use chalk paint. I would just lightly sand the tile assuming it has a shiny finish and use a good brand of chalk paint.