Help with some Roman coins

If anyone could identify these coins i'd really appreciate it, I have had these for a long time but never figured it out!
Many thanks in advance.
Values would also be usefull as I will probably be selling some of them soon.

The bottom left one is a coin of emperor Tacitus in the later 3rd century:

Obv.: IMP C CL TACITVS AVG
Rev.: VIRTVS AVG

It is not in the catalogue, so far as I can tell.

The bottom right one is ─I *think*─ a coin of Constantius I before he became emperor ("NOB CAES") but I would need to examine it closely with a magnifier to be sure.

I think this is a very similar one in the catalogue. Or else you can compare with other coins of the Tetrarchy by scrolling down on this page.

You might find the top right one by following this link and scrolling down.

The top left one is a textbook example how NOT to clean a coin. (Of course, I assume you got it like this, not that you tried to clean it!)

Thank you!
The bottom right is actually my favourite so thank you for such an indepth identification!

Цитата: "Camerinvs"​The top left one is a textbook example how NOT to clean a coin. (Of course, I assume you got it like this, not that you tried to clean it!)

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Hello,

It is a follis of VIRTVS EXERCIT type, mint by Licinius Ist.

In fact, any Roman coin has necessary been cleaned at a moment or another, should it be only to remove the earth off of it : indeed, roman coins can not come from drawers or walls originally, but have been all found in the earth.

Simply, there are good cleanings and bad cleanings. Look at the Tacitus' coin : it has been formerly cleaned, and even harshly cleaned, but it has then got a beautiful cabinet patina. Look also at this cleaning result of mine :

Цитата: "Quiquengrogne"​
​In fact, any Roman coin has necessary been cleaned at a moment or another, should it be only to remove the earth off of it : indeed, roman coins can not come from drawers or walls originally, but have been all found in the earth.

Simply, there are good cleanings and bad cleanings. Look at the Tacitus' coin : it has been formerly cleaned, and even harshly cleaned, but it has then got a beautiful cabinet patina. Look also at this cleaning result of mine :
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Exactly. The final result on this coin of Domitian is astounding ─ a little work of art.

The issue of cleaning should not be taken dogmatically. Even some modern coins sometimes need to be cleaned, though without removing the patina. I use acetone to remove ugly yellow residue of scotch tape (see this thread, including the last post).

A few weeks ago I won on eBay a scarce US 1913D Buffalo nickel for about a fifth of the catalogue value. The surface was covered in some green "slime". It just needed to be gently wiped to reveal the real patina.