In the engineering world, 'white metal' often refers to a kind of bearing material based on tin.
The equivalent in the household world would be pewter.
And in fact, the photo looks a bit like pewter.
Pewter is an alloy of tin and other metals. The 120 might indicate the ratio of tin to other ingredients, but I would not bet on it, as the number would normally be below 100
I'd not put pewter into a dishwasher. it is a soft metal with a low melting point. You would run a high risk of bending.
The following is from Wikipedia:
"It is traditionally composed of 85–99% tin, mixed with copper, antimony, bismuth, and sometimes lead, although the use of lead is less common today. Silver is also sometimes used. Copper and antimony act as hardeners while lead is more common in the lower grades of pewter, which have a bluish tint. Pewter has a low melting point, around 170–230 °C (338–446 °F), depending on the exact mixture of metals."