I noticed this in a different forum. Seems like it could be relevant to this thread.
https://www.kitcomm.com/showpost.php?p=1147318&postcount=1Fake 100oz Engelhard Silver Bars from China
We only have some preliminary information right now, but thought it would be good to get it out ASAP.
About a month ago we got a report of strange 100oz Engelhard silver bars. They were underweight, and owner thought that they might have just been shaved, but then was concerned that they might be filled with lead. He had received them from a supplier in China.
It turns out that the dimensions are off (the bar is only 21mm thick, versus the 27mm of a standard Engelhard extruded 100oz silver bar; it is also a bit wider). The sides are not tapered, like a real one (where the length and width on the top of the bar are longer than on the bottom, because of the slanted sides). The bottom has some pitting on it. The weight is low, at around 2,800g (versus 3110+g).
We got a sample today, and tested it with an ultrasonic thickness gauge. It tested as definitely not being silver, and likely being lead (a velocity of sound of 2,250m/s rather than silver's 3,650m/s). Putting the bar in a plastic bag and tapping it with a hammer produced a 'clunk' type of sound, rather than a ringing sound.
These may soon appear on the popular auction site, if they haven't made it there yet.
We hope to provide more details (including pictures and such) soon, but I wanted to give people a quick heads-up.
[EDITED 04 Jan 2011 TO ADD:]
We now have a page at
http://About.Ag/Lead100OunceBars.htm that has all the details, including a close-up picture, and details on how to detect these.
We also have a page at
http://About.Ag/UltrasonicThicknessGauge.htm that details how to test using ultrasonic thickness gauges.
And, we have a YouTube video at
http://www.youtube.com/watch?v=_T8fdshyEek showing how we tested the bar with an ultrasonic thickness gauge.