I observe that you speak in your valuable manual of Aureolin as a _very slow-drying_ colour when ground with oil; finding, in use, that _Roberson's_ Aureolin dries, on the contrary, extremely quick--it is always absolutely dry the next day, and I use no vehicle but Bell's Medium, _i.e._ linseed and oil of spike and turps.--I wrote to ask him what he grinds the colour in. He answers "_pure linseed oil without the addition of any drier._" This puzzles me. Where is the solution? Are there different kinds of Aureolin? When you have a leisure moment send me a post-card. * * * * * Among the madders in your handbook _scarlet_ madder does not appear; I hope it is not a treacherous colour; I use it freely, but only mixture with other _dark_ colours, to give them richness. I also use cadmium _red_; is that wrong? A line on a post-card will greatly oblige. _P.S._--Of course I only use cadmium red when I want a _very_ deep orange in drapery or sky--nothing could replace it. * * * * * _Feb. 2, 1885._ Here is a little problem: I thought all _burnt_ colours were _ipso facto_ sound. Roberson tells me that burnt white (Chremnitz do.), a lovely colour _like ivory_, plays most amazing tricks, darkens and lightens again in rapid succession. WHY? When you are in Long Acre make him show you his samples. * * * * * Thanks for your letter. I don't use any particular colours other than those you mentioned in your lectures, although I thought of trying deep yellow madder again; I used to like it very much. I suppose you have the list--it is a very long one--of Edouard's colours. Smith is his agent here (14 Charles Street, Middlesex Hospital). I use one or two colours (Tadema I think _all_) from Mommen's in Brussels; his burnt sienna is _superb_. Asphaltum would reward study; it was _universally_ used by the Venetians, and seems never to have cracked with them. I am very glad that you are steadily pursuing your collection of specimens and experiments, which I hope will by degrees become an exhaustive one, and of infinite value to the profession. _Grounds_, too, will deserve much attention. * * * * *