Just adding an update to this re the red cased M & S vase mentioned in the original post - normally this gets dusted (sorry - that's the d-word!), but as it had a dead spider stuck in the bottom of it, I decided it was due for a warm bath instead. Imagine my surprise when washing it to find that the red simply floated off! It was an applied coating on the inside of the vase. Stopping washing before it all parted from the glass, and allowing the glass to cool (as I was bemused by the idea of a coating inside a vase that was water soluble - it's a vase for flowers for goodness sake!) I tested it with cold water and found the surface didn't float off, it only happened with the warmer water. So however it was coated in the inside, the coating appeared to be stable for its use with cold water and flowers, and unstable in warm water being bathed! I now have a completely clear glass vase with a pierced bubble base... (pic to follow!)