Severus Alexander (222-235 A.D.) - Silver Denarius - 18.93mm, 2.59gr
Obverse - IMP ALEXANDER PIVS AVG
Severus Alexander, his laureate and draped bust right
Reverse - PROVIDENTIA AVG
Annona, standing head-left, holding grain ears and anchor,
a modius at her feet.
Severus Alexander
Here's the before/after (or should I say after & before) cleaning picture for this coin, which came in a group of 9 semi-uncleaned
denarii - 4 of Severus Alexander, 4 of Elagabalus and one of Julia Mamaea, found in the UK.

Method of cleaning:
1. Repeated baths in citric acid (three parts demineralized water to one part citric acid powder),
each time followed by a bath in demineralized water. Baths lasted several hours each.
2. Several 30 second dips in something called "zilver snelglansdip" / "silver fast-shine dip",
an ammonia based solution -not silver polish!- from  HG International,
once again followed by a bath (lasting several hours) in demineralized water.

A no point did I touch this coin with any tools like brushes, picks, etc!
Severus Alexander
Minted in Rome 231 A.D.
Reference:
Mattingley, Sydenham, & Sutherland, "Roman Imperial Coinage", Volume 4, Part 2 (RIC), p89, nr. 252(b)
Sear, D.R., "Roman Coins and their Values" (RCV Millennium Edition), Volume 2, p649, nr. 7923
Sear, D.R., "Roman Coins and their Values" (RCV 4th Revised Edition), p221, nr. 2232A (and plate 7)
Cohen, H, "Descriptions Historique des Monnaies frappees sous l'Empire Romain" (C), Volume 4, p453, nr. 508
Seaby, H.A. & Sear, D.R. , "Roman Silver Coins" (RSC), Volume 3, p143, nr. 508a
Carson, R.A.G., "Coins of the Roman Empire in the British Museum", Volume 6 (BMC), p196, nr. 813-4
Van Meter, D., "Handbook of Roman Imperial Coins", p213, nr. 54/3
Suarez, R., "Encyclopedia of Roman Imperial Coins" (ERIC),  p228, nr.19 variety B05 (B05, O02, R099, T005, M2)
Quality: Very Fine+