One Penny , Sg 44- Is The Stamp Overinked ?

Could someone please give his oppinion, on this UK,SG 44,used one penny stamp. The Queen's Head clearly shows white on it's back . Is this caused by overinking from it's front side and is this a variety or not ?

No, it is not overinked, no, it is not a variety like an 'ivory head.' It is just the thickness of the paper / ink suffusing the paper.

The cancellation, also, is very visible from the back: same reason.

The cancellation may be for Radstock in Somerset having been assigned a number used earlier in Eardisley in Herefordshire. Afterwards, it was assigned to Houghton-le-Spring, Durham.

Thank you,for the information . It also looked me a bit little to the "Ivory head" type stamps .I was not very certain that's why I asked. Isn't the thickness of the paper suppose to be the same ? I don't know how often can it be seen ,is this something common?

This was handmade paper. It varied in thickness. An ivory head is much more pronounced and called 'ivory' head because it looks very much like ivory. It was caused by the ink, usually the Prussiate of potash in it suffusing the paper in a distinct way. Your example appears to be primarily a case of thickness of the paper resulting in translucence.

The additional information which you've shared is also very useful.
I didn't looked at the cancel at all, I was focused on the stamp itself and the image showing on the back of the stamp.

A, fellow collector told me in tath potash was put at the ink mixture and then applied on the back of the stamp , preventing falsification of the stamp.
He also said me ,tath's it's most often seen in blue color. I know tath this concerns mainly the "Ivory head" type of stamps.

That fellow collector got the wrong end of the stick - or paper, in this case -.

Prussiate of potash was a constituent of the original red inks. It made the ink fugitive. The combination of the wet paper and the Prussiate of potash in the ink resulted in suffusing of the Prussiate of potash colouring the back of the stamp blue where ink was applied. As the unprinted (or lightly engraved) part of the stamp's face did not result on blueing of the paper, it left a blank area where the head was. This looked like an ivory cameo against a 'blue' background called 'ivory head.'

This is not the same as using Prussiate of potash to make the ink run if an attempt was made to clean off the cancellation. This coloured the paper blue. Applying it to the back of the stamp should make you ask whether the Post Office was trying to poison its customers. The back is what you lick to make the stamp stick to the mail item, not where you forge the stamp image on, or remove the cancellation from. At some time, there was a trial with the use of Prussiate of potash for that purpose. That has nothing to do with the 'ivory head' or application to the back that is completely useless unless you want to poison people.