That's not bad, I lost my plastic one but the idea is good since writing on labels does get washed away sometimes.
Just one thing did pop into my mind when I was thinking that maybe the aluminium could be harmful.
Orchids as far as I know are quite sensitive to metals, I tried to google aluminium and nothing came up so maybe aluminium is safe but if you have read enough care guides you do come across the odd one warning of copper toxicity, air plants are especially sensitive to it apparently.
This article mentions in the second paragraph on ph to avoid galvanised pipes:
"Be sure to use plastic or polythene pipes if you have acid water as the acid can act as a solvent and release zinc or copper from galvanized and copper pipes and cause toxicity to plants."
GROWING ORCHIDS - Angela van Rooyen | Orchids SA
Can you make plastic labels instead? They would work just as well, would be a shame if the labels cause a problem.
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