At first, this denarius of Faustina I seems unremarkable, but its existence is fascinating and raises more questions than it answers. I'd love to hear your thoughts, and by all means, post anything you feel is relevant! Faustina I, AD 138-140. Unofficial imitative issue?, 3.19 g, 17.6 mm, 6 h. Ca. AD 140-160? Obv: DIVA FAVSTINA, bare-headed and draped bust, right. Rev: PIETATI(?) AVG, Pietas, veiled and draped, standing left, dropping incense from right hand onto lighted altar and holding box in left hand. Refs: Cf. BMC p. 67, † note, RSC 234b, CRE 113 and Strack 462 (Budapest), all of which read PIETAS AVG. Is this a fourrée imitation or a solid silver, official issue? If this is an official issue, it must read PIETAS AVG, for no coins with a PIETATI AVG reverse legend and a standing figure sacrificing over an altar appear until the reign of Pescennius Niger. Many coins depicting Pietas were issued for Faustina I after her death, and this coin superficially resembles RIC 394a/BMC 311-314, but that coin has the obverse inscription, DIVA AVG FAVSTINA, whereas the obverse on this coin bears the later DIVA FAVSTINA inscription. The coin with this combination of obverse legend and reverse type is extremely rare. An exhaustive internet and print search revealed only the following three examples (the first two are die-matches): Gorny & Mosch Giessener Münzhandlung Auction 181, 13.10.2009, lot 2210 (3.25 g). Macho & Chlapovič Auction 2, 28.4.2012, lot 70 (2.6 g). Temeryazev, S. A., and T. P. Makarenko. The Coinage of Roman Empresses, 113, pp. 48-49. So, if the coin reads PIETAS AVG and if genuine, it would be rare indeed. Unfortunately, my coin is not a die match to either of these examples, which would clarify the reverse inscription and argue for its authenticity. If the reverse inscription reads the dative-case PIETATI AVG, then it must be an imitation/forgery. Denarii bearing the PIETATI AVG reverse legend are few and far between. The only coin issued with a PIETATI AVG legend in combination with a sacrificing figure on the reverse is a rare denarius of Pescennius Niger bearing the togate figure of the emperor sacrificing, not the female personification of piety, Pietas: Pescennius Niger, Antioch mint, RIC 68, BMC 311, p.79. Timeline Auctions, 26.02.2019, lot 3029. These coins of Niger are die-matches to each other and clearly very different from the reverse of my coin. So, if my coin is an imitation and reads PIETATI AVG, there appears to have been no coin ever issued to have served as an exemplar for the reverse! Factors supporting the coin is an official issue: The coin is of proper weight, 3.27 g, such as the Gorny & Mosch example. The reverse inscription isn't entirely clear and may well read PIETAS AVG. No coin was issued with PIETATI AVG that could have served as an exemplar for an imitative reverse die. The areas on the coin's reverse between the letters AV, and around the left hand holding the box may be patches of reddish-brown corrosion on the surface of the silver near an area of flan lamination and not an exposed base-metal core. Factors supporting the coin is an imitation: Weight is not a reliable indicator of authenticity. The style of the obverse portrait is somewhat crude. Try as I might to see PIETAS, it really looks like it says PIETATI. Try as I might to see a lamination flaw, it really looks like a crack in the plating between PIETAS' hand and the A in AVG, exposing a base-metal core. My wish list vis-à-vis this coin: Die-matched examples would come to light to clarify the reverse inscription and whether or not it's fourrée in manufacture. Experts, such as @curtislclay and @Barry Murphy might weigh in. I'd like to see the example in the Budapest Nationalmuseum cited by Strack.
Neat find, something I have never seen either. This may be wrong, could there be a chance it was overstruck with a Niger?
What an intriguing coin! I guess I lean toward unofficial due to style & that legend, but I can see why you're seeking advice! Here's a clearly unofficial eastern European imitation, in good silver. (Note the lamination defect on the obverse. If I were betting I'd say yours was in good silver too. Would be good to see the edge.)
There are many solid silver (of varying alloys) coins of the period. There is no reason to equate being unofficial with being plated or poorly made. The term I prefer is 'money of necessity'. When there is no reliable source of official, regular coinage, it is quite reasonable to do it yourself. Possibly it was even done with Imperial permission. We will never know. The coins below are neither official style nor plated.
Tentatively I would think "unofficial", mainly because of the crude obv. portrait that you point out. Hard to decide on the rev. legend, since the possible letters TI are both a little unclear. If we read PIETAS, the known legend, then there is a rather large gap between the sacrificing figure's head and the supposed S, and that supposed S looks more like an I anyway! On your coin and the one numbered 113 above, Pietas lowers her r. hand to drop incense on the altar; whereas on the other two denarii from the same die pair she raises her r. forearm and perhaps extends her fingers, as though in prayer. The Budapest coin may be this second variant, since Strack writes "r. Hand hebend", that is "raising her r. hand".
I have rephotographed this thing and have examined it with a good magnifier. I have convinced myself the reverse legend reads PIETATI AVG. The rust-colored areas on the reverse are on top of the silver, not inside defects in any plating. There is a lamination defect on the reverse at the 3:00 position. I think it's made of good silver (as @Severus Alexander suggests) but an unofficial issue, as @dougsmit and @curtislclay have opined.