Wow. @ancient coin hunter, I didn't even know Valerian or Gallienus issued sestertii. Your point about what the tariffing would look like, after the initial, Gallienian nadir of debasement, has to be dead on. @dougsmit is likely right, although I have no idea when the infamous silver-washed tin issues began; could it be early (enough) in Gallienus' sole reign? Meanwhile, the Gallic sestertii (and multiples) are conspicuously associated with Postumus' reintroduction of antoniniani with appreciable silver content. ...Then again, I wonder if the replacement of bronze with tin as the metallic underlay might have been predicated on the initial appearance of the tin, after the silvering had worn off. Might it have looked more 'silvery' than it does after most of two millennia? One might involuntarily think of 1943 Lincoln pennies, and how lousy the zinc tends to look, after a minute or two. ...Um, horn-tooting ensues. When I was 13, I won 'Best of Show' at a local coin show, for a display about Roman debasement, c. Hadrian into the 4th century. There was an Old, Old monograph on the subject, maybe ANS, by Augustus John, on which I relied heavily. (Now long gone.) Surely a lot more has been done on the subject since then.
Asses are considerable more difficult to find than sestertii. Here's a joint-reign example from Gallienus, to supplement the sole reign Salonina I posted earlier in the thread: 25mm, 10.14g
I have a restored sestertius of postumus 260-269 AE Sestertius. Lyons.(?) IMP C POSTVMVS PF AVG, laureate, draped bust right. FIDES MILITVM, Fides standing left, holding two standards.
I have one of these. I guess I never considered his brass coinage to be even scarce let alone rare but with the OP's example in such splendid condition I can see why one might be just that. I don't think there's much unusual about this pedestrian example but here it is. It is supposed to have been struck, joint reign, ca. 254 AD and is supposed to read IMP C P LIC GALLINU (S AVG). A male figure on reverse (Virtus, Mars, the emperor?) holding a spear4 and shield with the obligatory SC. It weight is 12.23 grams, close to the weight of a Julio-Claudian As. How the mighty have fallen. It is R.I.C. 248, Sear 10530
Mine. Not too great. Too bad the obverse isn't as good as the reverse: Gallienus. 253-268 AD. Æ Sestertius (29mm, 14.44 gm, 10h). Rome mint. 1st emission, 253-254 AD. Obv: Laureate and cuirassed bust right. Rev: Concordia standing left, holding patera and double cornucopia. RIC V 209; MIR 36, 15dd.
Unfortunately I sold all of my post Phillip sestertii - which of course I regret. However, I did notice that the art work in many of the coins from the post Phillip era is quite impressive - see the web-site “Four Bad Years” for some outstanding examples - also the coins in the RIC plated for the period - the artistry is stellar!