I did triple thick years ago. I mostly just used contact cement for glass to adhere the ink down. You will still get a shadow, but it will keep it stable. Bally ink was thicker than most of the other manufacturers. I would press it flat, & weight it down. When dry I would flow over the cracks, & after dried use a black sharpie to hide the cracks if needed (do a little to see if your happy). I know lots of operators, & techs that would just spray paint the back a color over missing ink. Mostly on Gottlieb, Williams, & Stern glass.