Plastic milk bottle tops lids caps (Kids Art craft school). They will be washed, although you still might find some that aren't spotless. Most of them are quite clean when they come to me (especially the reds), but I pick out any dirty ones and do wash them in soapy water, although not every one will come out perfectly clean.
If it looks like some quantities aren't in stock you can give me a message, it may be that I have enough or I can get the extra ones from my supplier if you don't might waiting a little longer. I don't get many purple or orange though as they are be quite hard to come by!
If you are using them for something interesting then please let me know as I sometimes pass on the stories to the parents as we are a charity and it encourages people to collect for me.