If anyone revolutionized violin technique (mainly for the left hand) it was Niccolo Paganini (1782-1840).  

For a violinist, it is incredible that at that time it was possible to play everything that he wrote, but it is also unthinkable that anyone would write something that could not be performed.  So, to play the extensions, fingered octaves, double harmonics (which demand great independence among the fingers), tenths, etc. can only be explained by having an exceptionally large hand, and that was not the case.  According to what the Genovese violin professor, Renato De Barbieri, told me, at the time of the anniversary either of his birth or his death, his casket was opened and it was evident, as the body was embalmed, that his hands were curiously relatively small, contrary to what drawings and sculptures of the time had made us believe. For that reason, the explanation is that Paganini suffered from the syndrome of hyper laxity of the ligaments, which some circus artists also have.  

But returning to music, Paganini wrote 6 violin concertos of his own inspiration, many works for solo violin, or with piano accompaniment. For the most part, he drew his themes from different operas (Moses, Ipalpiti, etc) and wrote some increasingly difficult variations, although I must say, interesting and entertaining (for the listener). The themes of the concertos are his own and very inspired, although the accompaniment is quite simple and not elaborate. But even this could have been voluntary, in order to not distract the listener from the melody and virtuosic interest.

In any case, in my opinion, the most important and absolutely brilliant works are the 24 Caprices for solo violin. In addition, they have an extraordinary didactic content. I find them beautiful. Simply beautiful, but of course, they must be well performed. They contain inventiveness, a melody. Let’s say they usually contain one part that is melodic and another virtuoso. I am thinking of number 3, 4, 6, 7, 11, 13, 15, 20, etc. And the didactic aim is always present. But what is written must be respected, not facilitated. For example, in the fast section of nº 11, the composer indicates “contro” which means it must all be performed with the bows reversed.

Many violinists from the last century published editions of these Caprichos in which they corrected them and even changed some notes, but without the slightest improvement in the melodic line. Today there is an edition that is totally faithful, that of Renato de Barbieri, which includes them exactly as Paganini wrote them. So this is the one I recommend.  

The truth is that I could write for hours about this work, but as always, I don’t want to be too technical, and only try to tell what the music tells me.