It may appear somewhat droll for any one to answer a question on which he has _not_ had experience; but I beg to offer as a _suggestion_ to PHOTO, that if he wishes to use collodion pictures for the purpose of dissolving views, he should first copy them in the camera as transparent objects so as to _reverse_ the light and shade, then varnish them with DR. DIAMOND'S solution of amber in chloroform, when they will bear the application of transparent colours ground in varnish, such as are used for painting magic-lantern slides. GEO. SHADBOLT. _Gutta Percha Baths_ (Vol. vii., p. 314.).--In "N. & Q." for March 26, I ventured to recommend to H. HENDERSON gutta percha, as a material for nitrate of silver baths. I did this from a knowledge that hundreds of them were in use, but chiefly because I have found them answer so well. In the same Number the Editor gives MR. HENDERSON very opposite advice; and, had I seen his opinion before my notes appeared, I should certainly have kept them back. But it is, I think, a matter of some importance, especially to beginners, to have it settled, whether gutta percha has the effect of causing "unpleasant markings" in collodion pictures or not. With all due deference to the Editor's opinion, I do not believe that gutta percha baths are injurious to the finished picture. I have never any markings in my glass positives now, but what may be traced with certainty to some unevenness in the film or dirtiness on the glass. And I hope that the number of beginners who are using gutta percha baths, and who are troubled with these unpleasant markings (as all beginners are, whether they use glass or gutta percha), will not, without some very careful experiments, lay the fault upon the gutta percha. In the Number for April 2, the Editor thanks me for what he is pleased to call "the very beautiful specimen of _my skill_." This was a small glass positive, which I sent him in accordance with an offer of mine in a former note. Now, _that_ was rendered sensitive in a gutta percha bath, which I have had in use for months; and I think I may appeal to the Editor as to the absence of all unpleasant markings in it. Probably it may be a good plan for those who make the baths for themselves to adopt the following simple method of cleaning them at first. Fill the bath with water, changing it every day for a week or so. Then wash it with strong nitric acid, and wash once or twice afterwards. Always keep the nitrate of silver solution in the bath, with a cover over it. Never filter, unless there is a great deal of extraneous matter at the bottom. If glass baths are used, cemented together with sealing-wax, &c., I imagine they might be as objectionable as gutta percha. The number of inquiries for a diagram of my head-rest, &c., from all parts of the kingdom--Glasgow, Paisley, Manchester, Leicester, Leeds, Newcastle, Durham, &c. &c.--proves the very large number of photographic subscribers "N. & Q." possesses. I think, therefore, it