I can, assuming the metallurgist is using the standard alloys. Silver is the whitest of those three metals, but dulls very quickly, and is so soft it soon picks up scratches. White gold has a tinge of yellow. Platinum looks grayer and duller than the rest. However…platinum and white gold are both commonly played with rhodium, a very shiny white sister-metal to platinum, so they can look exactly alike. Platinum settings tend to be more “solid-looking”, thicker shanks and prongs, but that is simply jewlery-making convention. If I am unsure whether something is white gold or platinum, I heft it; platinum is significantly heavier.
I am the daughter of a jeweler, and have worked in the buisness for about 8 years (not currently). I can also almost always tell on sight the difference between 10k, 14k, 18k, 22+k, gold plate and gold filled. We used to test gold with (IIRC) hydrocloric acid; you scratch the metal and drip some on. Green bubbles and smoke means goldplate or goldfilled. Dark discoloration means 10k. No reaction means 14k or above.
“Lustrium” was a variant of stainless steel. My class ring was in it too.
And do you really think this will spank a Great Debate?
“Eppur, si muove!” - Galileo Galilei