Several friends of mine who use distemper, and he amongst the number, tell me that by putting a preparatory coating of distemper over thoroughly dry oil, you can with perfect safety interpose a layer of _painting_ in distemper between two paintings in oil--an extremely valuable thing for us _for recovering quality_. * * * * * _January 31, 1890._ Many thanks for your valuable letter. I have had the information entered in a little book, where I keep the outpourings of your wisdom on matters chemical. Thanks also for the card, in which you give me a somewhat long name for my Gomme Dammar. I suppose in an appeal to a chemist the _first_ portion would suffice. * * * * * _February 14, 1890._ Many thanks for your valuable note. I may say in passing that the specimen of "Ruby Madder" sent by Mr. Laurie appears to me to be inferior in brilliancy to both the Rose Madder and the Madder Carmine furnished by Messrs. Roberson; and I have no reason to doubt that the latter colours are perfectly trustworthy. It will give me great pleasure to receive the dedication of your book, which I look forward to seeing with pleasure, and using with profit. * * * * * _May 19, 1890._ Many thanks for your note, which seems to open up an interesting point. I gather from what you say that the mode of _manufacture_ of a colour may affect its drying properties over a range extending from drying very slowly to drying very rapidly; and I shall be much interested in hearing what your experiments lead to under this head. * * * * * _January 30, 1891._ Many thanks for your letter. I see that I had better wait for a final opinion until the few months have expired which you still require as tests of permanence. Meanwhile, I am a little unhappy to see in the case of colour after colour the expression "semi-permanent." I do not quite know what that means. Let me know _at your leisure_ whether it means permanent under certain conditions, and, if so, what; or merely in a general way that the pigment stands, but only pretty well. The Rosso Saturno I quite understand is to be set aside.