Here are some more stofnamen (substance names) in Dutch with 3 letters:
- Aarde (earth)
- Blut (blood)
- Brons (bronze)
- Glas (glass)
- Goud (gold)
- Hars (resin)
- Hout (wood)
- Izer (iron)
- Klei (clay)
- Kwik (mercury)
- Lood (lead)
- Melk (milk)
- Mist (fog)
- Papier (paper)
- Plas (plastic)
- Roest (rust)
- Slijk (mud)
- Stof (dust)
- Water (water)
I hope this is more helpful!