Edith Heath Ceramics Rose Dinner Plates Lot of 3

Three beautiful vintage Heath Ceramics 11 1/4" diameter dinner plates in the pretty Rose Peacock pattern. This has the Heath stamp on underside center, plus a handwritten incised mark that is hard to read but looks like "13 + 8 La + Lav" -- I wonder if this could be the formula for an experimental glaze used on this plate? I don't know much about Heath pottery. They're in great vintage condition -- I see a few light utensil marks near the center but no other issues.