TRANSACTIONS OP THE SECTIONS. 13 



of the highest conceivable fullness and richness both of tint and detail, the colour in 

 this case being a superb velvety brown. This extreme richness of effect is not pro- 

 duced except lead be present, either in the ingredients used, or in the paper itself. 

 It is not, as I originally supposed, due to the presence of free tartaric acid. The 

 pictures in this state are not permanent. They fade in the dark, though with very 

 different degrees of rapidity, some (especially if free tartaric or citric acid be present) 

 in a few days, while others remain for weeks unimpaired, and require whole years 

 for their total obliteration. But though entirely faded out in appearance, the pic- 

 ture is only rendered dormant, and may be restored, changing its character from 

 negative to positive, and its colour from brown to black (in the shadows) by the fol- 

 lowing process : — A bath being prepared by pouring a small quantity of solution of 

 pernitrate of mercury into a large quantity of water, and letting the sub-nitrated 

 precipitate subside, the picture must be immersed in it (carefully and repeatedly 

 clearing off all air bubbles), and allowed to remain till the picture (if anywhere visi- 

 ble) is entirely destroyed, or if faded, till it is judged sufficient from previous expe- 

 rience ; a term which is often marked by the appearance of a feeble positive picture, 

 of a bright yellow hue, on the pale yellow ground of the paper. A long time (seve- 

 ral weeks) is often required for this, but heat accelerates the action, and it is often 

 complete in a few hours. In this state the picture is to be very thoroughly rinsed and 

 soaked in pure warm water, and then dried. It is then to be well-ironed with a 

 smooth iron, heated so as barely not to injure the paper, placing it, for better security 

 against scorching, between smooth clean papers. If then the process have been suc- 

 cessful, a perfectly black, positive picture is at once developed. At first it most 

 commonly happens that the whole picture is sooty or dingy to such a degree that it 

 is condemned as spoiled, but on keeping it between the leaves of a book, especially 

 in a moist atmosphere, by extremely slow degrees this dinginess disappears, and the 

 picture disengages itself with continually increasing sharpness and clearness, and ac- 

 quires the exact effect of a copper-plate engraving on a paper more or less tinted 

 with pale yellow. I ought to observe, that the best and most uniform specimens 

 which I have procured have been on paper previously washed with certain prepara- 

 tions of uric acid, which is a very remarkable and powerful photographic element. 

 The intensity of the original negative picture is no criterion of what may be ex- 

 pected in the positive. It is from the production, by one and the same action of the 

 light, of either a positive or a negative picture according to the subsequent manipu- 

 lations, that I have designated the process, thus generally sketched out, by the term 

 umphitype, — a name suggested by Mr. Talbot, to whom I communicated this singu- 

 lar result ; and to this process or class of processes (which I cannot doubt when 

 pursued will lead to some very beautiful results) I propose to restrict the name in 

 question, though it applies even more appropriately to the following exceedingly 

 curious and remarkable one, in which silver is concerned. At the last meeting I 

 announced a mode of producing, by means of a solution of silver, in conjunction 

 with ferro-tartaric acid, a dormant picture brought out into a forcible negative im- 

 pression by the breath or moist air. The solution then described, and which had, 

 at that time, been prepared some weeks, I may here incidentally remark, has re- 

 tained its limpidity and photographic properties quite unimpaired during the whole 

 year since elapsed, and is now as sensitive as ever,— a property of no small value. 

 Now, when a picture (for example an impression from an engraving) is taken on 

 paper washed with this solution, it shows no sign of a picture on its back, whether 

 that on its face be developed or not ; but if, while the actinic influence is still fresh 

 upon the face (i. e. as soon as it is removed from the light), the back be exposed for 

 a very few seconds to the sunshine, and then removed to a gloomy place, a positive 

 picture, the exact complement of the negative one on the other side, though wanting of 

 course in sharpness if the paper be thick, slowly and gradually makes its appearance 

 there, and in half an hour or an hour acquires a considerable intensity. I ought to 

 mention that the "ferro-tartaric acid" in question is prepared by precipitating the 

 ferro-tartrate of ammonia (ammonio-tartrate of iron) by acetate of lead and decom- 

 posing the precipitate by dilute sulphuric acid. 



P.S. When lead is used in the preparation of amphitype paper, the parts on which 

 the light has acted are found to be in a very high degree rendered water-proof . 



