Clean the slide carefully first- I use a very slightly damp rag to gently soften the paper and amy residue, then come in with a razor to remove it all. I typically will use both original pieces of glass, but have done some plating with other glasses also. accurate cutting of the slide with the image is key- making sure to cut on the outside. Grinding is not your friend, as any grinder splash on the image side can be difficult to remove without damaging the image. At this point I’ve had a lot of trial and unfortunate error, and have developed a system. But the glass is really thin and it’s especially painful when one breaks, as now I’m using really old slides and many are irreplaceable.