Interesting reply Cumbrian...
To answer the question, I would personally use westmoreland green, of course random.
welsh £1.70 a slate? is that for best? or standard?
I am still interested in availability.....
Family roofing history.... funnily enough my grand father was a Thatcher, his father was a slater..and I've been a roofer for 35 years since school.
Camster
Good Spanish slates are Villar Del Ray or Del Carmen Firsts there are more.. available through SIG possibly exclusively.. might be wrong there..
the very very best go not into the UK but europe where requirements are in fact stricter.
I have seen a spanish slate side by side a welsh and the difference was near zero.
Now I would never knock a welsh slate, just saying the world is round not flat.