“Electroforming” indicates it’s something used in the electroforming metal deposition process (the technique of building up metal layers on a conductive surface using an electrolyte solution and DC current). 

The numbers 17gm‑21 typically suggest something like:

• 17 g — the weight of the chemical powder/metal salt in one pack, and

• 21 — possibly 21 packets/items or a product code.