1790

 Although not specified as such, Priestly's price-weight is entirely consistent with platina ore at avirdupois.  Where 8 ounces avd = 7.292 English Troy Ounces,

"Richard Knight and His Production of Malleable Platinum"(PMR Vol. 29, #1, 1985; p. 30)

Priestley was also sufficiently interested in platinum to purchase a modest amount; his claim for compensation after the destruction of his house and laboratory on July 14, 1791 includes the item “Half a pound of platinum £ 2 8 s. 0 d.”

c.1790/1: 1 Troy Ounce of platina (ore) = £0.33

c.1790: 1 Troy Ounce Platinum (mfg) ~ Fr 105 (USD$ )

Citation: Naturgeschichte und Technologie: für Lehrer in Schulen und für Liebhaber ...;Carl Philipp Funke (1792 ) p.673

 

"The price {of Platinum manufactures} is slightly lower than works in gold."

"Platina Gefässe in Paris von Jeanty billig zu kaufen"

You unquestionably have long known that some excellent chemical artist edit the Platina as other metals, even found time not so long ago: but that work had been so multiplied darinn now, you would think no. Meanwhile, I can still assure you that at Janety - of against very cheap prices includes snuff-boxes, watch chains, spoon, toothpick boxes, Löhtröhrchen, and everything you could want from a similar work only wishes and orders, (Marchand Orfevre, Rue de l'Arbre Sec) pure platinum, extremely clean and tastefully worked once can get. The Preiss of commodities depends, like, gold and silver, according to the severity and type.

c. 1917 anecdote. A full-weight 1789 2-Escudo weighs 6.76 g., .8985 Fine Au

The Specific Gravity for an older true 2-Escudo should have been 17.655, or 17.18 for a coin just .875 Fine Au.  Also, given the loss of weight from wear, the original Platinum forgery 'new' likewise should have had a Specific Gravity ~19. At this SG, the counterfeit would likely have been approx. 5% Au (Surface), 90% Pt and 5% Cu