Any INTENSE(!) left hand pizz studies?
God save the queen pizzicato variation is for me the most difficult. After you can play this, you can probably play anything :)
Maybe just a little too intense.
Souvenir de Sarasate is where a lot of students encounter LH Pizz for the first time. LH Pizz is the worst thing ever introduced to the violin. Not even Heifetz could make it sound good.
Guess Heifetz didn't practise enough.
In Zapateado, Joseph Hassid's LH pizz is so perfectly blended with the spiccato bowed notes that I didn't realize they weren't pizz until I heard Heifetz's recording!
Ricci's book on left hand technique covers it well. Sevcik too-maybe on the 4th book, supposedly about double stops that also covers double harmonics? (I forgot.) I believe mastering different challenges on the instrument helps with the "easier" obstacles. That said, I generally don't find LH pizz difficult, just annoying depending on the work (ascending is always more difficult, but intelligent practice conquers all.) I did do LH Pizz with Ricci's book when I was younger, and it wasn't never too difficult afterwards, though some players have an amazing, very resonant LH pizz.
My ability to do LH Pizz vanished over time in proportion to my ability to snap my LH fingers audibly - I guess I just got too old.
So that's the issue...
I actually can't snap my fingers since childhood. Don't know if it's just not knowing how to do it, or maybe if I am just "flawed" (a combination is more likely.)
Sevcik Op. 1, Part IV, No. 19. Looks like a "warm up", and there are trickier passages, but playing the whole page without trouble likely means you can easily develop the LH pizz technique to be used elsewhere.
The trick to a resonant LH pizz is that the finger stopping the note has to be held down very firmly.