NOTATIO

An interesting quasi-S-shaped slur from the copyist's autograph of Chopin's Etude op 25 no 10:
The first French edition:
The first German edition and most modern editions:
The first English edition:
Chopin wants the middle voice brought out and played expressively against the octaves, something that often doesn't happen in performance. I think that the S-shaped slur communicates this best and will engrave it as:

In my opinion, your slur have a such unusual movement that I get lost in a way. It is visually interfering with one ledger line and two staff lines (LH) or three staff lines (RH), which is quite a lot for connecting one tone apart.
I prefer the first edition, or Chopin's MS.

And yes, it is not an easy "puzzle".

John, how does your solution look without the colour? Can you please post a black and white screenshot as it might be easier to judge.

I think I probably agree with OCTO, but would like to give it more thought.

Thanks, David. I forgot to remove the display colors. Here it is in black and white:
So you both do not like the solution in the first English edition? Or is it just my slur that you don't like?

OCTO., I didn't understand what you meant by "Chopin's MS" and also "first edition" since there are three first editions. I thought the S-shaped slur as shown in the first English edition and in the copyist's autograph and in my engraving was Chopin's solution. Of course, this assumes that the "partial" S slur was the copyist's interpretation of a real S-shaped slur in Chopin's lost autograph. At least that is what the engraver of the first English edition thought, and so do I.

Hm... sorry for confusion.
I doubt that Chopin's slur is S shaped (now I realize it is The copyist's autograph you speak about, not Chopin). At least not that in RH. For me it looks as very delicate U shape.
About The first edition, I meant by the French edition (that was the first picture displayed). Sorry again, I was reading at my tablet.
The problem with S shaped slur, except above I said, is that it follows the "secondary" melody. I find it a bit confusing, for my taste.

Would be great to hear others views too.

Ah... Now I understand, OCTO. The slur appears to follow the triplet line. What a good point. The very thing that I thought was so good about the S slur, the room provided by the shape of the triplet melody, is actually a negative.

Back to the drawing board. I'll see what I can do with the French edition style. That is not going to be easy.

That's how Peters (Ed. Scholtz/v. Pozniak) does it:

I prefer it because I think it is more prominent and obvious. Opposed to that the S-shaped slur is subject to more "optical competition", interferring with the stafflines and beeng squeezed between lots of notes.

Thanks, Christof. In general, that is the way it has been done in modern editions for the all the good reasons you mentioned. What is a little different in your example is the degree of offset of the middle voices, which helps relate the slur to the note heads. But it does interrupt the even flow of the triplets, so I might try something a little less extreme but in that style, as a last resort.

I am trying to preserve certain communicative features of the autographs that get generally get lost in engraving. Chopin (as seen through the lens of the his copyists, who generally duplicate slavishly what they see in the autograph) might more conveniently done the standard thing here, but he seems to be concerned about pointing out the middle voice with the slur. I am hoping to come up with something that does this without creating a reading problem.

I agree with Christof - your reasoning is perfectly sound but I feel the slur will just get lost in the stems and barlines unless it's, say, made unusually heavy in comparison.

The problem actually intensifies when the theme appears an octave higher and where it becomes harder to relate the slurs to the second middle voice note with the traditional (German) slurring. Here are three versions in which I increased the offset along the lines of Christof's example.

Ex.1 I toned down the curvature of the S slur.
Ex.2 I did my best to relate the end of the slur to the second middle voice note. But the proximity of the upper slur works against this in the RH.
Ex.3 This is the closest to the copyists autograph and the French first edition, but it doesn't quite work in my opinion.
I guess my head is with Ex. 2, but my heart is with Ex. 1. I found Ex. 3 hard to make work in Finale.

Schonbergian, thanks for your comment. I am concerned that if the S-slur were heavier, OCTO.s objection about the slur obscuring reading might be in effect even more. Note that the French and English first editions use unusually thin slurs. I am hoping that the unusual shape in itself distinguishes it from the staff lines.