Photo slate problems

[pw66]

Never printed photo slates before today.
First one off the press was very good, but the second one camie out very mottled in the centre ( same settings/different image than the first). The printing around the edge was clear and sharp.
The problem area was the darkest part of the design (so most ink coverage). All I can think is maybe not letting the transfer dry long enough or to much ink. I used 'best photo' setting on the Epson 1500. Maybe drop the print quality?
Any help would be gratefully received.
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[Justin]

What inkset are you using in the 1500? What time and temp are you pressing at?

Are you using a pad inbetween the slate and the platen?

Loads of info already on here about slates, quick search should help

[pw66]

Face down, on silicon sheet, 400sec at 185 degrees. Sublinova and S race paper.