172 HISTORY OF PHOTOGRAPHY. 



the highest couceivable fulhiess and richness both of tint and detail, the color 

 in this case being a superb velvety brown. This extreme richness of effect is 

 not produced 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 foj weeks 

 unimpaired and require whole years for their total obliteration. But, though 

 entirely faded out in ai)pearance the picture is only rendered dormant, and may 

 be restored, changing its character from negative to positive and its color from 

 brown to black (in the shadows), by the following process: A bath being pre- 

 pared by pouring a small quantity of solution of pernitrate of mercury into a 

 large quantity of water and letting the subnitrated precipitate subside, the pic- 

 ture must be immersed in it (carefully and repeatedly clearing off the air 

 bubbles) and allowed to remain till the picture (if anywhere visible) is entirely 

 destroyed, or, if faded, till it is judged sufficient from previous experience, 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 

 (several 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 thor- 

 oughly 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 ])aper, 

 placing it, for better security against scorching, between smooth cleaff papers. 

 If, then, the process has been successful, 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 spoilec^, 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 acquires the exact effect 

 of a copperplate 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 preparations 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 

 expected in the positive. It is from the production, l)y one and the same action 

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

 quent manipulations, that I have designated the process thus generally 

 sketched out by the term "AiiipJiitype," a name suggested by Mr. Talbot, to 

 v/hom I communicated this singular result; and to this process or class of 

 processes (which I can not doubi: when pursued will lead to some very beautiful 

 results) 1 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 produ- 

 cing, by means of a solution of silver in conjunction with ferro-tartaric acid, a 

 dormant picture brought out into a forcible negative impression 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 retained its limpidity 

 and photographic properties cpiite unimpaired during the whole year since 

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

 v.'hen a picture (for example, an impression from an engraving) is taken on 

 paper washed with this solution it shows no sign of a pictui'e on its back, 

 whether that on its face he 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 

 lack be exposed for a very few seconds to sunshine and then removed to a 



