The only way to absoloutely tell is a specific gravity test, I would not trust XRF, sometimes people buy those machines used etc latest software not installed or whatever, but I will tell you this I had a guy test some rings for me he said all plated gold nothing real, went to a guy that just got the latest and confirmed gold, so I of course sold to him. 40% will weigh 24.592 grams +/- 4% it does not look wore enough to render weight on clad at 22.69 grams. also it is only 21% silver innercore, I don't know what XRF readings he was getting but he may not understand the readings he was seeing. check weight, if still unsure sound test it, if still unsure do a specific gravity if you have the capabilities, you can not tell by color alone. There was errors of 71-D on silver and also 77-D on silver certified by ngc or pcgs should get you 5k+ depending on grade, good luck!!!