Metal ERA deposit receipts could begin in 10 gram and and 20 gram RECTANGULAR tokens, made of high-carbon "zinc alloy steel" (the preliminary proportions are 97.5% iron, 2% carbon, 0.2% zinc and 0.3% nickel).

This alloy would contain the minimum set of easily accessible elements while achieving the following ten main characteristics:
Strength: High
Hardness: High
Corrosion resistance: High
Hardness: High
Wear resistance: High
Melting point: High
Appearance: Bright
Machinability: Low
Cost: Low
Supply chain risk: Low

Most steel includes chromium or molybdenum, but we want to reduce supply chain risk; also the unique alloy makes counterfeiting more difficult. Using X-ray fluorescence testing of samples, anyone can test of the fidelity of the ratios of the elements in the finished product, through an X-ray fluorescence lab or use of a hand-held tester https://alloytester.com/xrf-steel-tester.

Currently I am also verifying how feasible and costly it would be to have alphanumeric character serial numbers engraved on each token by microscopic laser engraving.

Regarding the graphic design of the 10 gram and 20 gram tokens (see sample "coin" images attached) our graphic design needs to be:
(a) pluricultural
(b) plurilinguisic
(c) plurigeographical
... please add other design criteria you reckon to be important.