Yes I think it most likely is Poirson. As to which one, it depends on the date. I now see 1836 and 1896 at the same time. Now, for me, its like looking at one of those optical illusions where I see a duck and a rabbit at the same time.

As they say: "It doesn't matter what you are looking at, its what you see. And we see with our brains through our eyes." 

So how to settle on a date from that pencil writing?

If it says 1836 then the violin could be said to be possible made by Pierre Poirson 1732-1742 (a "fair maker") who worked in Mirecourt. But does the violin look that old? I'm not experienced enough to have a clue. But the pegs could well be original 18th century ones because they are old and they are Baroque.  

If the writing says 1896 then it could be a Elophe Poirson violin. Then what of the old boxwood baroque pegs?

Did they actually "brand" the violins with a hot iron, or were the letters scribed-in and then blackened? 

What I don't understand is the "liver spot" marks on the face of the violin. The violin has cleaned up with just a tiny amount of water with a minute fraction of rice vinegar added, but those spots won't budge a single bit. They have impregnated the varnish. My daughter's teacher had a lovely sounding old Italian violin on trial from a renowned violin dealer some years ago. It had the same marks on it. 

Can anyone shine any light on this?

Gordon Shumway said
Something that is intriguing is, given how much wear the fingerboard has suffered, why is there no wear where the bridge has been?

If you hunt around, you'll find examples of this in extremis.

  

I am wondering if the table (face of the violin) is just possibly a later replacement addition. Could it just possibly be a cut and shut violin? The varnish on the back appears definitely more autumn leaf yellowy than that on the table, which under certain lighting conditions appears more yellowy-golden-amber. The varnish is intriguing. On this one there is no way I can tell if its oil or spirit varnish. 

Gordon Shumway said
Incidentally, anyone with a spare £250 burning a hole in their pockets can buy a copy of this

  

The back could be a late 19th century addition only if (a)  the pencil writing reads 1896 and not 1836, or (b) it was never an honest note in the first place. Do either of those conclusions seem likely? 

The mystery violin is finally back together in one piece.

What I never realised is that it is a genuine baroque violin. The fingerboard being a fair bit shorter and the back being noticeably flatter and other proportions different to a Strad model. At some point in time someone added a small wedge under the fingerboard to elevate it closer to a Strad. model. But the neck is genuine and there is no graft. 

If it is a Poirson violin, then taking account of the old pencil writing inside of 1836 - and working on the premise that the pencil writing is repairer's signature - then it could be a Pierre Poirson (1732-1742) violin. It can't be an Elophie Poirson violin, because that maker only made violins between 1876 and 1918. 

The fact is is a genuine baroque (or late 18th early 19th transitional?) violin points me initially towards Pierre Poirson. But that is just an initial start. I could be completely wrong. 

I tried the violin with Dominant strings and a modern tailpiece and a normal bridge (Aubert) but it was very unresponsive on the D string. I had to really tune the bridge to get anything like a good tone. So I tried a baroque bridge, Dominant strings and longer vintage late baroque length tailpiece. It sounds fantastic - I tuned it first to the classic Baroque 415 Hz and then tried it at the modern standard 420 Hz. Both sound great but I have tuned it now to 420. I added an interesting minimal antique chinrest (baroque violin players don't tend to use a chinrest) that works very well. I place a handkerchief over it to protect the instrument's varnish from my chin when playing. 

The violin is incredibly sweet, colourful mellow and has good volume and brightness on the A string. Beautiful soulfulness and resonance on the D string. I set the bridge at 4mm on the E-string to 5mm on the G string. 

Now I will have it played and assessed by a professional violinist. 

Then it will need to be re-homed.