I just checked it out with Quattro Pro
Assuming the Rio prices for PMC are quoted for ounces avoirdupois,
quoted cost of PMC at Rio of $28.95 per oz corresponds to $1.041 per
gram, while the half oz pkg. at $14.95 works out to $1.055 per g.
At $35.25 per 20 g. pkg., the Art Clay works out to $1.763 per g.,
while the 50 g pkg. at $84.95 is $1.70 per g.
But if the units are in Troy ounces the Rio price for PMC price is a
bit lower, because there are 31.1035 g per Troy ounce, but only 28.345
per avoirdupois ounce. In that case, the price quoted for Rio is $0.95
per oz in the 1 oz pkg., or $0.96 in the half ounce pkg.
But if the cost of Art Clay quoted by Kathie Bishop is accurate, the
picture changes dramatically. At $27 for 20 grams, the Art Clay costs
$1.35 per gram, while the larger pkg. of 50 grams at $65.20
corresponds to about $1.30 per g.
A better comparison of costs should be based on the silver content of
each product, in pennyweights per gram or some such.
Useful about weights and measures is found at: