text: how can i tell if a ring is real platinum?   platinum is extremely dense (heavy for its size).  not only will it not float in water, it will sink faster than lead!  its extremely difficult to measure the size of a small ring using the water test-i know, ive tried it and i have access to a laboratory.  platimun, like gold, is resistant to normal acids.  if your ring resists corrosion from hydrochloric or sulphuric acid, its platinum.