A few years ago, while on holiday, I bought a couple of painted wine glasses. After looking at them and examining them I thought I could do them just as well.
I collected various pieces of interesting or unusual glass, – usually quite cheaply from car boots or charity shops – and bought glass paint and tubes of Cerne Relief (a ceramic liner) mostly from Hobbycraft. Most art shops sell glass paint, and you do need to have separate brushes for this as it will ruin them. I also liked using lead on my glass, the kind used on windows. (Used on the glass on the right in the above group, and on the glass on the left below.)