Hi guys thanks for your replies so far..I have been digging it out from an area where the stream has run round a bend and left a great buildup of clay so getting a really good yield which is very satisfying!.. I have already screened out twigs and pebbles and quite fine grit with an old wooden sided sieve I got in a job lot of craft tools at an auction. It doesn't say how fine the mesh is but I'm guessing at 40 or bigger. So by the looks of it I will need a at least a 60 if not a 100. I'll now search up local clay as Rockhopper suggested. Thank you!