THE 
 
 CALOTYPE 
 
 FAMILIARLY EXPLAINED; 
 
 BEING 
 
 a Cmti'se on its jerts antr t^ses, 
 
 AND THE 
 
 METHODS OF PREPARING THE SENSITIVE PAPER, 
 
 AND TAKING 
 
 PICTURES BY THE AGENCY OF LIGHT. 
 
 BY 
 
 W. RALEIGH BAXTER, M.R.C.S. 
 
 LICENTIATE OF APOTHECABIES* HALL, DUBLIN AND LONDON ; 
 LECTURER ON NATURAL HISTORY, MATERIA MEDICA, &C., &C. ; 
 MEMBER OF THE MBDICO-CHIRURGICAL SOCIETY, &C., &C. 
 
 LONDON c 
 
 PUBLISHED BY H. RENSHAW, 356, STRAND. 
 1842. 
 
Frinted at the Steam Press of A. W. Evans, Craven Yard, Drury Lane 
 
TO THE DIRECTORS OF THE ROYAL 
 POLYTECHNIC INSTITUTION. 
 
 Gentlemen, 
 
 I beg leave respectfully to inscribe the following 
 sheets to you. Having heard the admirable lecture delivered 
 by Dr. Ryan on the subject of the Calotype, it occurred to 
 me that there existed a necessity fora manual which would 
 guide the student in this branch of the Photographic art : I 
 have endeavoured to supply this want in as familiar and con- 
 densed a form as possible. I was captivated with the style in 
 which the lecturer treated this subject, and the entire success 
 of all his illustrative experiments ; and for his general courtesy 
 as well as for the pleasure and information I have derived 
 from time to time from his prelections, I take this opportunity 
 of tendering my grateful thanks. 
 
 Of the general character and tendency of the Institution 
 under your efficient direction, I cannot speak too highly. 
 My opinions are entirely identified with those of a public 
 writer, who gives his in the following curt phraseology : — 
 
 “ This Institution, (the Polytechnic namely,) and such men 
 as Dr. Ryan, have done more to premote a taste for abstract 
 science than the entire British Association.'' 
 
 I remain, Gentlemen, 
 
 Your obedient servant, 
 
 VT. RALEIGH BAXTER. 
 
THE CALOTYPE. 
 
 The art of Photography is one of the most pleasing and 
 curious results of chemical philosophy, and certainly not 
 one of the least useful. Those who have beheld on the field 
 of a camera obscura the minutely perfect reflection of a 
 landscape, with its rivulet, its well-clad trees, and its animated 
 groups, must have regretted that it was but a shadow doomed 
 to exist only for a moment, while the light shone or the in- 
 strument remained stationary. Photography, however, and 
 especially that modification of it immediately under consi- 
 deration, termed the Calotypb, enables us to render perma- 
 nent the objects thus reflected. To accomplish this, no 
 tedious or troublesome process is necessary ; unlike the crea- 
 tions of the artistes pencil, the pictures thus produced are not 
 the result of long and tiring manipulation. In a moment our 
 work is over — our desires accomplished. 
 
 In order that our readers, and especially such as have hi- 
 therto paid but little attention to such subjects may form some 
 idea of the the mode in which light acts so as to produce pic- 
 tures upon prepared paper or metallic plates, rendered sensitive 
 to its influence, we shall for a short time refer to certain well- 
 known effects of light on plants, animals, and chemical com- 
 pounds. 
 
6 
 
 Li^ht i8 the cause of colour in plants, in animals, and in 
 minerals. The ruby, the humming-bird, and the violet, are 
 enriched from the same source. We shall now endeavour to 
 explain this in a familiar manner. A ray of light, although 
 perfectly white to the eye, consists, in fact, of a bundle of 
 rays,” of different colours, and possessed of different functions, 
 while on the absorption or reflection of the various rays de- 
 pend the varieties of all coloured bodies. It is to Sir Isaac 
 Newton that we owe this discovery. The instrument em- 
 ployed ft»r the purpose of decomposing a ray of light is a 
 triangular piece of glass called a prism, and the party-coloured 
 figure produced by its agency is called the prismatic spectrum. 
 The effect produced by means of the prism is owing to the 
 different refrangibility of the seven coloured rays of light. 
 The violet ray suffers the greatest refraction, and is therefore 
 found at the top of the spectrum, while the red, being least 
 refrangible, fuund at the bottom. The other rays are dis- 
 posed according to their different degrees of refrangibility. 
 If the spectrum be divided into 360 equal parts, to correspond 
 with the 360 degrees of the circle, the violet colour will be 
 found to occupy 80 of the parts, the indigo 40, the blue 60 
 the green 60, the yellow 48, the orange 27, and the red 45, 
 
 We may remark here, that Sir David Brewster has proved 
 that the term primary colours, applied to the seven coloured 
 rays in the spectrum, is incorrect, as there are in reality only 
 three primary ones, blue, yellow, and red, while all the others 
 are merely modifications of them. 
 
 When bodies reflect or turn back all the ra\ s of light which 
 fall upon them, they are termed white ; but, on the contrary, 
 when all the rays a^e absorbed, we call the bodies thus ab- 
 sorbing the light, blac^, indicating, in fact, a total absence of 
 colour. Thus, again, every substance in nature will appear 
 of that particular colour of the spectrum which its construe- 
 
7 
 
 tion will enable it to reflect. Thus, for example, the colour 
 called blue, or red, is produced in bodies by an absorption of 
 all the other rays except the blue or red, which are reflected, 
 and therefore become visible to the eye. 
 
 However, colour is not the only property which light be- 
 stows even upon plants. Taste, odour, and combustibility, 
 are derived from the same source ; and “ the spicy gums of 
 Araby,” the medicinal plants of southern America, and the 
 odoriferous resins of the East, owe their qualities to the 
 abundance of light falling upon their native soils. Such, too, 
 is the influence of light upon the organism of plants, that in 
 sunlight they pour forth streams of vital air, or oxygen, 
 while in the shade, on the contrary, they exhale poisonous 
 carbonic acid. 
 
 If a plant bearing flowers be placed near a window, the 
 flowers will all seek the light, approximating as nearly as 
 possible to the window. Those flowers, too, which bloom on 
 the side nearest the window are always of a more beautiful 
 colour and healthful appearance than those more remote from 
 the light. Again, if a plant, hitherto bearing beautiful flowers 
 and green leaves, were transported to a spot to which light 
 had no access whatever, it would not only become sickly, but 
 would actually in time be rendered colourless, and so altered 
 in appearance as no longer to present the distinguishing fea- 
 tures of the family to which it belonged. There are many 
 cases on record where the seeds and roots of well-known 
 plants have accidentally found their way into dark mines and 
 coal-pits, and have there vegetated, but so altered have the 
 products been, owing to the absence of light, that even bota- 
 nists have failed to recognise their species. The outside of 
 many of our esculent vegetables are beautifully green, while 
 the heart is colourless ; for instance, the cabbage and the 
 lettuce. The colour of the outside is owing to the influence 
 
8 
 
 of light; the whiteness of the heart is owing to its absence. 
 Market gardeners are well aware of these facts, and in order 
 to preserve these vegetables white and tender, they are covered 
 as much as possible from light during their growth. This 
 operation is termed bleaching in the cabbage and lettuce 
 it is produced by tying the leaves of the plants together ; in 
 celery it is produced by covering as much of the vegetable as 
 possible by means of earth. 
 
 Light has a great effect upon the health and appearance of 
 animals as well as plants. This is very apparent in the poor 
 creatures who toil in our coal-mines ; and the squalor and 
 dwarfishness to be seen in the nariow courts of the metro- 
 polis may be traced as much to the absence of light as to the 
 imperfect ventilation of the place and the insufficiency of 
 food. The animals found in the polar regions are almost des- 
 titute of colour, being merely of a dingy whiteness; but the 
 reverse obtains among the inhabitants of the tropics. There 
 the birds have a plumage rich . and varied in colour ; indeed, 
 the animal and vegetable productions of those countries 
 where light and heat are most abundant, are more numerous, 
 precocious, and extensive in their dimensions. We must not 
 omit to mention the different effects of light upon the colours 
 of the living and the dead plant. That very agency which 
 gave to the leaf or flower its richness of hue during life, the 
 moment it has ceased to exist, actually becomes a bleaching 
 agent, and robs it of its beautiful tints. Most of the colours 
 employed for dyeing are of vegetable origin, and every house- 
 wife knows what havoc sunlight makes upon her papered 
 rooms, her curtains, and her carpets. Even such of the pre- 
 cious gems as owe their value to the richness of their colours 
 are injured by exposure to light; the ancients noticed this 
 fact in connection with the opal and the amethyst especially. 
 
 Having noticed the action of light upon plants and animals. 
 
9 
 
 we shall consider some of its effects upon certain chemical 
 combinations. Here, however, the field that opens upon us 
 is so extensive, that our principal difficulty will be how to 
 choose from so large a number of examples those which are 
 most striking. There is not a substance,” remarks Fourcroy, 
 
 which in well-closed glass vessels, and exposed to the sun’s 
 light, does not experience some alteration from this cause. 
 Among these, the mineral acids, the metallic oxides or calces, 
 vegetable powders, and volatile animal oils, are most singularly 
 changed. Metallic oxides in general, especially those of mer- 
 cury, become of a deeper colour by exposure to the sun; as 
 may be seen by observing painters’ colours preserved in powder 
 in the shops. The mineral acids by the same treatment be- 
 come higher coloured, more volatile and fuming. Metallic 
 salts grow black, and animal oils take an obscure brown.” 
 Many of these effects of light were first noticed by the cele- 
 brated Scheele, and next by Berthollet. 
 
 However, the first parties who noticed the effect of the sun’s 
 rays upon metallic compounds were the alchemists. They 
 were in the habit of filling a bottle with a salt now called the 
 chloride of silver, but called then luna corneay or horn silver, 
 a compound exceedingly sensitive to light, and after cutting 
 out certain devices upon black paper, it was laid upon the 
 bottle, and the whole exposed to the light. Where the sun's 
 rays had had access to the compound, the salt was blackened, 
 while the portions protected by the paper remained wh’te. 
 But although the alchemists had by this experiment actually 
 stumbled upon the threshold of the discovery of Photography, 
 yet so intent were they upon their absurd search after the 
 philosopher’s stone, that every thing which did not promise 
 them so hopeless a result was thrown aside as useless. 
 
 The first person who seems to have had any notion of Pho- 
 tography, was Mr, Wedgwood, whose mini was led to the 
 
10 
 
 subject by observing that light blackened a solution of nitrate 
 of silver, or lunar caustic. If any of our readers have had 
 at any time occasion to employ this salt, they no doubt have 
 noticed that paper, or linen, or even the skin of the body, if 
 touched with it, in a short time blackens. This is owing to 
 the action of light ; for if the objects thus touched were kept 
 in the dark, no change would be perceptible. It is on this 
 account that marking ink becomes gradually blacker. The 
 principal ingredient in that preparation is nitrate of silver, and 
 being a sensitive compound, is acted upon by the light. A 
 knowledge of these facts led Mr. Wedgwood to perform his 
 first experiment, which was thus conducted : — 
 
 He took a solution of nitrate of silver, and having covered 
 a piece of writing paper with it, exposed it behind a painting 
 on glass to the sun^s rays. Of course wherever the rays of 
 light could fall upon the paper, it blackened ; the portion pro- 
 tected remained white. Now, could he have arrested the 
 further influence of light, and thus have fixed the picture, he 
 would have accomplished nearly all that was necessary — a8 
 in our day the employment of a more sensitive compound than 
 nitrate of silver gives a difference in degree, and not in prin- 
 ciple. But although Mr. Wedgwood, together with Sir 
 Humphrey Davy, experimented carefully, the object of fix- 
 ation could not be accomplished, and the whole ended in 
 failure. 
 
 In the first volume of the ‘^Journal of the Royal Institu- 
 tion/» published in 1802, there is a short memoir on the sub- 
 ject, by Sir Humphrey Davy. In this memoir the talented 
 V liter gives Mr. Wedgwood the credit of having originated 
 the first notion of the art. The following record of the failure 
 of these two great men is extracted from the memoir just 
 quoted : — The copy of a painting, immediately after being 
 taken, must be kept in an obscure place. It may indeed be 
 
11 
 
 examined in the shade, but even in this case the exposure 
 should be only for a few minutes. No attempts that have been 
 made to fix the pictures have as yet been successful. They have 
 been covered with a thin coating of fine varnish, but this has 
 not preserved them. The images formed by means of a camera 
 obscura have been found to be too faint to produce an efiect 
 upon the nitrate of silver in any moderate time. To copy 
 these images was the first object of Mr. Wedgwood, but all 
 his numerous experiments proved unsuccessful.’^ 
 
 About this time the scientific world was busily engaged in 
 ascertaining the existence and locality of the chemical rays 
 of light. It was discovered by M. Ritter and Dr. Wollaston, 
 that if the muriate of silver were exposed in a spectrum to 
 the least refrangible rays, or those which give the greatest 
 amount of heat without light, no effect was produced upon 
 it ; but when exposed to the most refrangible ray, the violet, 
 it was rapidly blackened, and even beyond the violet ray, in a 
 space perfectly invisible to our eyes, the darkening effect was 
 most apparent. Thus as there are invisible rays beyond the 
 red, giving heat without light, so are there beyond the violet 
 ray others which, although beyond the range of vision, have 
 the maximum intensity of chemical action. These interesting 
 researches were verified by Berard, Lubeck, and Berthollet, 
 Sir William Herschel, Sir Henry Englefield, Sir Humphrey 
 Davy and others ; nor should we omit to mention the experi- 
 ments of our countrywoman, Mrs. Mary Somerville, who de- 
 monstrated that a needle might be magnetized by exposing it 
 to the violet ray, a fact originally announced by Professor Mo- 
 richini, of Rome, verified by Professor Configliachi, at Pavia, 
 and M. Berard, at Montpellier. 
 
 It was at one time supposed that terrestrial or artificial light 
 possessed no chemical rays, but this is incorrect. Mr. Brande 
 found that although the concentrated light of the moon, or 
 
12 
 
 the light even of olefiant gas, however intense, had no effect 
 on chloride of silver, or on a mixture of chlorine and hydro- 
 gen, yet the light emitte I by electrized charcoal blackens the 
 salt, and explodes the gases. At the Royal Polytechnic In- 
 stitution pictures are daily taken by means of sensitive paper 
 acted upon by the Drummond light. The longest time re- 
 quired is 30 seconds, and the paper is sensibly darkened in 
 one second. Nor is there any attempt made in this case to 
 concentrate the rays ; no reflector is used. 
 
 After the failure of such men as Wedgwood and Davy, it is 
 not to be wondered at that the subject should have been 
 dropped. In fact, nothing more was heard of it for thirty 
 years, although during a portion of that time, both here and 
 abroad, several persons had resumed the search for success. 
 
 It appears that M. Niepse, of Chalons on the Soane, com- 
 menced his researches in 1814. His early attempts seem to 
 have been marked with but small success, for he pursued his 
 experiments alone for ten years. He then became acquainted 
 with M. Daguerre, who was at that time busily engaged in a 
 kindred pursuit, and in 1839 the process termed Daguerreo- 
 type was published to the world. However, six months before 
 the French philosophers had published their discoveries, Mr, 
 Fox Talbot had communicated to the Royal Society his method 
 of rendering paper sensitive, as well as his mode of fixation. 
 Thus both in France and England, at one and the same time, 
 unknown to each other, Talbot and Daguerre were pursuing the 
 same object, and each with signal success. Since then Mr. 
 Talbot has assiduously followed up his first discovery, by re- 
 peated experiments, and the result is the modification of the 
 process, termed the Calotype,from the Greek words signifying 
 ‘‘beautiful picture or image.” 
 
 The Calotype differs very materially from the earlier photo 
 
13 
 
 graphic processes in many points. We shall now proceed to 
 enumerate a few of the most prominent. The image formed 
 upon the Calotype paper is at first invisible ; for although the 
 object has been reflected on the paper in the camera, or even 
 has been in contact with it, yet on removing it from the light 
 no trace can be perceived. This certainly is the most myste- 
 rious part of the process, and one which arrests almost more 
 than any other the attention of the manipulator. Tne paper 
 prepared by this process is also vastly more sensitive ; how- 
 ever, this, as we have previously remarked, is a difference 
 rather of degree than of kind. The flxation of the pictures 
 is also so much superior, that it admits of a great number of 
 copies being taken from each camera picture, which could 
 not be done by the former method, at least not with any 
 certainty. 
 
 In taking an image in the camera by the common Calotype 
 process, the first impression is always a negative one. By a 
 negative picture we mean one in which the lights and shadows 
 arc reversed, giving the whole an appearance not conformable 
 to nature. For instance, if we were to copy a piece of black 
 lace, we should have in the first case white lace upon a dark 
 ground ; but upon taking a second copy, upon sensitive paper, 
 we should then have what is termed a positive image, confor- 
 mable to the original ; viz., black lace upon a white ground. 
 In sitting for a portrait, the same result would take place if 
 the common Calotype mode were employed ; and although Mr. 
 Talbot has pointed out a method of taking positive pictures at 
 once, yet, as it is somewhat complicated and difficult, we would 
 strongly recommend the experimenter to take images by the 
 common mode first, and then recopy them upon sensitive paper. 
 
 In order to obtain a positive copy, it is best not to employ the 
 Calotype paper, as it is too sensitive. The common jffiotogra- 
 phic paper, prepared as follows, will answer the purpose more 
 completely : — 
 
14 
 
 Dissolve 25 grains of common salt (chloride of sodium) in 
 one ounce of distilled water ; soak the paper in it some time, 
 and then dry between blotting paper. Next dissolve 90 grains 
 of crystallized nitrate of silver in an ounce of distilled water, 
 and brush the paper with it twice, drying it by a fire 
 between each washing. Keep it in the dark until wanted for 
 use. Before taking the positive copy, cover the paper con- 
 taining the negative image with white wax to render it trans- 
 parent, so that the light may pass more readily through it. 
 This may be done by scrapin g the wax upon the paper, and 
 then, after placing it between two'other portions of paper, 
 passing a heated iron over it. 
 
 Preparation of the Calotype Paper, 
 
 In describing the mode of rendering paper sensitive by the 
 Calotype process we shall quote Mr. Talbot's own words. 
 
 First part of the Preparation of the Paper. 
 
 I dissolve 100 grains of crystallized nitrate of silver in 
 six ounces of distilled water ; I wash one side of the paper 
 with this solution with a soft camel hair-brush, and place a 
 mark upon that side by which to know it again. I dry the 
 paper cautiously at a distant fire, or else I leave it to dry 
 spontaneously in a dark place. Next I dip the paper in a 
 solution of iodide of potassium, containing 500 grains of that 
 salt dissolved in one pint of water. I leave the paper a 
 minute or two in this solution. I then take it out and dip it 
 in water. I then dry it lightly with blotting-paper, and finish 
 drying it at a fire, or else I leave it to dry spontaneously. 
 All this process is best done in the evening by candle light. 
 The paper thus far prepared may be called, for the sake of 
 distinction, iodized paper. This iodized paper is scarcely 
 sensitive to light, but nevertheless it should be kept in a port- 
 folio or some dark place till wanted for use. It does not spoil 
 by keeping any length of time, provided it is kept in a port- 
 folio and not exposed to the light. 
 
15 
 
 Second Part of the Preparation of the Paper. 
 
 This second part is best deferred until the paper is wanted 
 for nse. When that time is arrived I take a sheet of the 
 iodized paper and wash it with a liquid prepared in the fol- 
 lowing manner: — Dissolve 100 grains of crystallized nitrate 
 of silver in two ounces of distilled water; to this solution 
 add one-sixth of its volume of strong ascetic acid ; let this 
 mixture be called A ; dissolve crystallized gallic acid in dis- 
 tilled water, as much as it will dissolve (which is a very small 
 quantity) ; let this solution be called b. When you wish to 
 prepare a sheet of paper for use, mix together the liquids, a 
 and B, in equal volumes. This mixture I shall call by the 
 name of gallo-nitrate of silver. Let no more be mixed than is 
 intended to be used at one time, because the mixture will not 
 keep good for a long period. Then take a sheet of iodized 
 paper and wash it over with this gallo-nitrate of silver with 
 a soft camel hair-brush, taking care to wash it on the side 
 which has been previously marked. This operation should 
 be performed by candle light. Let the paper rest half a 
 minute, and then dip it into water, and dry it lightly with 
 blotting paper: and, lastly, dry it cautiously at a fire, holding 
 it at a considerable distance therefrom. When dry, the paper 
 is fit for use ; but it is advisable to use it within a few hours 
 after its preparation. 
 
 Note, that if it is so used immediately, the last drying may 
 be dispensed with, and the paper may be used moist. 
 
 “ Note 2. Instead of using a solution of gallic acid for the 
 liquid B, the tincture of galls diluted with water may be used 
 but it is not so advisable. 
 
 Use of the Paper. 
 
 The paper thus prepared, and which I name Calotype paper, 
 is placed in a camera obscura, so as to receive the image 
 
16 
 
 formed in thefrcus of the lens. Of course the paper must be 
 screened er defended from the light during the time it is being 
 put into the camera. When the camera is properly pointed 
 at the object, this screen is withdrawn, or a pair of internal 
 folding doors are opened, so as to expose the paper for the 
 reception of the image. If the object is very bright, or the 
 time is short, or the objects dim, no image whatever is visible 
 upon the paper, which appears entirely blank. Nevertheless 
 it is impressed with an invisible image, and I have discovered 
 the means of causing this image to become visible. This is 
 performed as follows : — I take some gallo-nitrate of silver, 
 prepared in the manner before directed, and with this liquid I 
 wash the paper all over with a soft camel hair-brush. I then 
 hold it before a gentle fire, and in a short time (varying from 
 a few seconds to a minute or two) the image begins to appear 
 upon the paper. Those parts of the paper upon which light 
 has acted the most strongly become brown or black, while those 
 parts on which light has not acted remain white. The image 
 continues to strengthen and grow more and more visible dur- 
 ing some time ; when it appears strong enough, the operation 
 should be determined and the picture fixed. 
 
 “ The Fixing Process. 
 
 “ In order to fix the picture thus obtained, I first dip it into 
 water. I then partly dry it with blotting paper, and then 
 wash it with a solution of bromide of potassium, containing 
 100 grains of the salt dissolved in eight or ten ounces of 
 water. The picture is then washed with water and then finally 
 dried. Instead of bromide of potassium, a strong solution of 
 common salt may be used, but it is less advisable. The pic- 
 ture thus obtained will have its lights and shades reversed. 
 With respect to the natural objects, viz., the lights of the ob- 
 jects are represented by shades, and vice versa. But it is easy 
 from this picture to obtain another, which shall be comform- 
 able to nature, viz,, in which the lights shall be represented 
 
17 
 
 by lights, and the shades by shades. It is only necessary for 
 this purpose to take a second sheet of sensitive Calotype 
 paper and place it in close contact with the first, upon which 
 the picture has been formed. A board is put beneath them 
 and a sheet of glass above, and the whole is pressed into close 
 contact by screws. Being then placed in sun-shine, or day- 
 light for a short time, an image or copy is formed upon the 
 second sheet of paper. This image or copy is often invisible 
 at first, but the image may be made to appear in the same 
 way that has been already stated. But I do not recommend 
 that the copy should be taken on Calotype paper ; on the con- 
 trary, I would advise that it should be taken on common 
 photographic paper. This paper is made by washing good 
 writing paper first with a weak solution of common salt, and 
 next with a solution of nitrate of silver. Since it is well known 
 having been freely communicated to the public by myself in 
 the year 1839, and that it forms no part of the present inven- 
 tion, I need not describe it here more particularly, although 
 it takes a much longer time to obtain a copy upon this paper 
 than upon Calotype paper, yet the tints of the copy are gene- 
 rally more harmonious and agreeable. On whatever paper 
 the copy is taken it should be fixed in the way already des- 
 cribed. After a Calotype picture has furnished a good many 
 copies it sometimes grows faint, and the subsequent copies 
 are inferior. This may be prevented by means of a process, 
 which revives the strength of the Calotype pictures. In 
 order to this it is only necessary to wash them by candle 
 light with gallo-nitrate of silver, and then warm them. This 
 causes all the shades of the picture to darken considerably, 
 ^while the white parts are unaffected. After this the picture 
 is of course to be fixed a second time. The picture will then 
 yield a second series of copies, and a great number of them 
 may frequently be made* 
 
 “ N ote. In the same way in which I have just explained that 
 a faded Calotype picture ma^ be revived and restored, it is 
 
 
18 
 
 possible to streng:then and revive photographs which hav c 
 been made on other descriptions of sensitire photographic 
 paper; but these are inferior in beauty, and moreover the 
 result is less to be depended on ; 1 therefore do not recom- 
 mend them. 
 
 “ The next part of my invention consists in a mode of ob- 
 taining positive photographic pictures, that is to say, photo- 
 graphies, in which the lights of the object are represented by 
 lights, and the shades by sharles. I have already described 
 how this may be done by a double process ; but I shall now 
 describe the means of doing it by a single process: I take a 
 sheet of sensitive Calotype paper and expose it to day-light, 
 until I perceive a slight but visible discoloration or browning 
 of its surface, — this generally occurs in a few seconds. I 
 then dip the paper into a solution of iodide of potassium, of 
 the same strength as before ; viz , 500 grains to one pint of 
 water. This immersion apparently removes the visible im- 
 pression caused by the light — nevertheless, it does not really 
 remove it; for if the paper were to be now washed with gall- 
 nitrate of silver, it would speedily blacken all over. The 
 paper, when taken out of the iodide cf potassium, is dipped 
 in water, and then lightly dried with blotting-paper. It is 
 then placed in the focus of a camera obscura, which is pointed 
 at an object. After five or ten minutes the paper is withdrawn 
 and washed with gallo-nitrate of silver, and warmed as before 
 directed. An image will then appear of a positive kind » 
 namely, representing the lights of the object by lights, and 
 the shades by shades. Engravings may be very well copied 
 in the same way, and positive copies of them obtained at 
 once (reversed, however, from right to left.) For this purpose 
 a sheet of Calotype paper is taken and held in day-light to 
 darken it, as before mentioned ; but for the present purpose it 
 should be more darkened than if it were intended to be used 
 in the camera obscura. The rest of the process is the same. 
 
 
19 
 
 The engraving and the sensitive paper should be pressed into 
 close contact, with screws or otherwise, and placed in the sun- 
 shine, which generally effects the copy in a minute or two. 
 This copy, if it is not sufficiently distinct, must be rendered 
 visible, or strengthened, with the gallo-nitrate of silver, as 
 before described. I am aware, that the use of iodide of potas- 
 sium for obtaining positive photographs has been recommended 
 by others ; and I do not claim it here by itself as a new in- 
 vention, but only when used in conjunction with the gallo- 
 nitrate of silver ; or, when the pictures obtained are rendered 
 visible or strengthened subsequently to their first formation. 
 In order to take portraits from the life, I prefer to use for the 
 ©bject glass of the camera, a lens, whose focal length is only 
 three or four times greater than the diameter of the aperture. 
 The person whose portrait is to be taken should be so placed 
 that the head may be ?s steady as possible, and the camera 
 being then pointed at it, an image is received on the sensitive 
 Calotype paper. I prefer to conduct the process in the open 
 air, under a serene sky, but without sunshine : the image is 
 generally obtained in half a minute, or a minute. If sun- 
 shine is employed, a sheet of blue glass sliould be used as a 
 screen to defend the eyes from too much glare, because this 
 glass does not materially weaken the power of the chemical 
 rays to affect the paper. The portrait thus obtained on the 
 Calotype-paper is a negative one; and from this a positive 
 copy may be obtained in the way already described. 
 
 I claim, first, the employing gallic-acid, or tincture of 
 galls, in conjunction with a solution of silver to render paper, 
 which has received a previous preparation, more sensitive to 
 the action of light. 
 
 ‘‘ Secondly, the making visible photographic images upon 
 paper, and the strengthening such image? when already faintly 
 or imperfectly visible, by washing them with liquids which 
 
20 
 
 have been previously acted upon by light. — Thirdly, the 
 obtaining portraits from the life by photographic means upon 
 paper. 
 
 Fourthly, the employing bromide of potassium, or some 
 other soluble bromide for fixing the images obtained.” 
 
 Dr. Ryan has noticed that in the iodizing process the sen- 
 sitiveness of the paper is materially injured by keeping it 
 long in the solution of iodide of potassium, owing to the 
 newly formed iodide of silver being so exceedingly soluble in 
 the excess of iodide of potassium as in a fgw minutes to be 
 completely removed. The paper then should be merely 
 dipped in the solution, and instantly removed. 
 
 There is another point, too, in the preparation of the iodized 
 paper in which Mr. Mitchell, Dr. Ryan^s talented asdstant, 
 suggests a slight deviation from Mr. Talbot’s method. In the 
 first instance he recommends the paper to be brushed over 
 with the solution of the iodide of pota^^sium, instead of the 
 nitrate of silver — transposing, in fact, the application of the 
 two first solutions. The paper having been brushed over 
 with the iodide of potassium solution, is washed in distilled 
 water and dried. It is then brushed over with nitrate of sil- 
 ver in solution, and after drying is dipped for a moment 
 in the solution of iodide of potassium — is again washed in 
 distilled water and dried. By this means the doctor states 
 that he obtains a more sensitive paper, and a more even 
 distribution of the compounds over the surface. 
 
 At the recent lecture of Dr, Ryan at the Royal Polytechnic 
 Institution he has been enabled to employ the strong glare 
 of the Drummond light during the preparation of the paper 
 without any injury accruing, merely by covering the flame 
 with a lanthcrn of yellow glass, although without such a me- 
 
21 
 
 dium the paper would be completely spoilt in half a second. 
 As in the preparation of the paper, both in the first and 
 latter stages, it will be necessary to have a little light — a shade 
 of yellow glass must be provided, which must be placed 
 around the lamp or candle. Light passing through such a 
 medium will scarcely affect the sensitive compounds, the 
 yellow glass intercepting the chemical rays. 
 
 Apparatus to he Employed, 
 
 After carefully preparing the various solutions according to 
 Mr. Talbotts plan, the following apparatus will be requisite: — 
 
 Two large shallow dishes to hold distilled water. We require 
 two as we must not wash the sensitive paper in the same, 
 water as that in which the fixed paper is to be placed. The 
 water in which the sensitive paper is washed will frequently 
 require changing, owing to the decomposition of the gallo- 
 nitrateof silver. 
 
 Several large camel-hair or badger brushes, without any 
 metal in contact with them. Each solution requires its dis- 
 tinct brush, which after use must be immediately washed in 
 distilled water. The one employed for the gallo-nitrate is 
 soon spoiled. 
 
 A graduated ourhce measure, in which to place the equal pro- 
 portions of solutions, A and B. 
 
 A large glass vessel, holding half a pint, for the solution of 
 bromide of potassium. 
 
 A quantity of white bibulous paper , cut to the size, or nearly 
 so, of the sensitive paper; in each stage of preparation dis- 
 tinct portions of bibulous paper must be used. If these be 
 kept separate and marked they can be again used for the same 
 
purpose ; but it wouTd not do to dry the finished picture, for 
 instance, in the same folds in which the sensitive paper had 
 been dried. 
 
 A camera obscuraf to take reflected objects. These may be 
 obtained for a very trifling sum from any of the opticians. 
 
 * A coupleof wooden frames and with hinges 
 
 so as to press the object to be copied (lace for instance) into 
 close contact with the sensitive paper. This apparatus may 
 be used for taking a positive picture from anegati>e copy. 
 
 A tin or pewter vessel, to hold hot water, upon which the 
 paper is to be laid after receiving the second coating of gallo- 
 nitrate. 
 
 A spirit lamp, in which naptha may be burnt. 
 
 A shade of yellow glass, to place between the light of the 
 lamp or candle, in which ease the preparation of the paper in 
 total darkness is necessary. 
 
 Tlie water in the vessel should nearly boil 
 Concluding Remarks, 
 
 Two years ago Sir John Herschel succeeded in producing 
 upon sensitive paper a coloured image of the prismatic spec- 
 trum : and since then he has, after repeated experiments, suc- 
 ceeded to a great extent in obtaining pictures in which objects 
 are represented in their natural colours. It would be prema- 
 ture to speculate upon the means he employs, but as his paper 
 recently read before the Royal Society will soon be published, 
 we shall then be in possession of facts and experiments so im- 
 portant and desirable. The application of this discovery to 
 various departments of the arts and sciences must be obvious. 
 
23 
 
 The botanist instead of employinc: his pencil day after day 
 in copying, and after all inaccurately, the minutiae of a plan, 
 or flower, need only call to his aid the Calotype, and in a mo- 
 ment he produces a copy rivalling the original in boldness and 
 detail. 
 
 To the meteorologist this discovery will be of extreme 
 utility, enabling him to ascertain with accuracy the amount 
 of light falling upon a given space in a given time. 
 
 Many of our scientific travellers have neither leisure nor 
 ability to employ the pencil, and therefore those at a distance 
 have to derive their only knowledge of scenery and buildings 
 abroad from the worded description of those who have visited 
 them. But by means of this art not only may the traveller 
 write of the places he has seen, but may bring home to his 
 countrymen the graphic representation of all that has caught 
 his attention, and this, too, by means of a camera, almost 
 small enough to be carried in the pocket. 
 
 M. Arago, in extolling the Daguerreotype, says, To copy 
 the millions and millions of hieroglyphics which completely 
 cover the great monuments of Thebes, Memphis, Carnac, &c., 
 would require scores of years and legions of artists. With 
 the Daguerreotype a single man would suffice to bring to a 
 happy conclusion this vast labour. Arm the Egyptian Institu- 
 tion with two or three of Daguerre^s instruments, and on 
 many of the large engravings in their celebrated work, the 
 fruit of our immortal expedition, vast assemblages of real 
 hieroglyphics would replace fictitious or purely conventional 
 characters. Again, these photographic delineations having 
 been subjected, during their formation, to the rules of geome- 
 try, shall enable us, with the aid of a few simple data, to as- 
 certain the exact dimensions of the most elevated parts, and 
 of edifices the most inaccessible." 
 
24 
 
 All this and more may he said of theCalolype, and we un- 
 derstand that the Prussian government is now fitting up an 
 expedition to Egypt, whose duty it will be to carry out, by Mr 
 Talbot’s process, the suggestions of the eloquent and scientific 
 Arago. 
 
 Mr.’ Collen, of Somerset-st., Portman-square, has been in the 
 habit of taking portraits by the Calotype for sometime. They 
 have a good, bold effect, and resemble mezzotinto engravings. 
 
 Printed at the Steam Press of A. W. Evans, Craven Yard, Drury Lane.