When we had the new roof put on the house I asked the builder to leave me any slate offcuts. I now have a huge stack in the garage and someone who is a dab hand with a tile cutter and happy to cut the slate into labels as I need them. They are so much nicer and more discreet than other labels. The white marker pen seems to work well on slate – I’m just checking them for durability, which so far is good despite the recent deluges.