Jeff Oestreich, Leach St Ives, and Minnesota, USA

Jeff Oestreich is still potting. Best to contact him directly

The photo of Jeff Oestreich's mark in the Pinterest link I posted earlier is off The Marks Project and is very similar

They are very similar but not quite the same. Unless he changed it slightly when he left Leach. I will try and contact him directly. But for him the one in the Marks Project would be upside down.

Yes, the Marks Project have got it upside down, and it's one of his later marks, when he returned to the US

I wrote back to the Leach museum with these images and they responded:

Hi Dan,
The mark of Jeff’s that I know is a JO over a line, inside a triangle, and he also did just a J.O as well with a dot, so he might have changed it quite often.
He has a website and a contact section so perhaps you could ask him?
He visits here every other year and by coincidence we have just sent off 9 boxes of pots to him from the pottery, (including some of mine!) for an exhibition in Minnesota.
Good luck with your pursuit of the truth!
Best wishes,
Joanna

I will send the images directly to him and ask.

Oh dear, they're hopeless, aren't they I follow them on FB and they're supposed to be putting together a database of ex-Leach apprentice details, but they don't seem to have got off to a very good start .

Here is Jeff's reply to my email.

"Oh my god! It is an oldie. Made while apprenticing at the Leach Pottery. 1969-1971. I had a ring made and I used it as a potters stamp. Yes, my stamp has changed a number of times"

Mystery solved.