@scarborian, will do, but as I remember (will look again at the tin I have popped) I was referring to the pronounced staining of the tobacco wrapper within the tin which you had mentioned in your post. I strongly suspect any crystals would be sugar, in one of its forms. Would you agree?
I rarely smoke mixtures (flakes, plugs and ropes - that's me) but I was so taken by Mlc's great picture of that old tin of King Charles that I will add a tin to my next 'My Smoking Shop' order and also, at your suggestion, a tin of the 1820 mixture.