I've used Armor Etch in the past with great success. I just followed the directions on the container. The only thing that would maybe have caused the sponge painting effect would be if there were oils on the glass. I know you can use china markers to and grease pencils to mask off areas that you don't want to etch. I'm thinking that maybe the glass wasn't 100% clean and dry when you applied the etching cream and that something was blocking the etching acid from getting through to the glass. Hope this helps!