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III。 PHOTOGENIC PROCESS ON PAPER。Method。The simplest mode is to procure a flat board and a square of glass； larger in size than the object intended to be copied。 On the board place the photographic paper ＇hipho_29。gif＇ with the prepared side upwards； and upon it the object to be copied； over both lay the glass and secure them so that they are in close connection by means of binding screws or clamps； similar to g。 g。 fig。 29。 Should the object to be copied be of unequal thickness； such as a leaf； grass； &c。； it will be necessary to place on the board； first； a soft cushion； which may be made of a piece of fine flannel and cotton wool。 By this means the object is brought into closer contact with the paper； which is of great consequence； and adds materially to the clearness of the copy。 The paper is now exposed to diffused daylight； or； still better； to the direct rays of the sun； when that part of the paper not covered by the object will become tinged with a violet color； and if the paper be well prepared； it will in a short time pass to a deep brown or bronze color。 It must then be removed； as no advantage will be obtained by keeping it longer exposed； on the contrary； the delicate parts yet uncolored will become in some degree affected。 The photogenic paper will now show a more or less white and distinct representation of the object。 The apparatus figured at 29 consists of a wooden frame similar to a picture frame； a piece of plate glass is fixed in front； and it is provided with a sliding cover of wood； c。； which is removed when the paper is ready to be exposed to the action of the light。 The back； d。； which is furnished with a cushion； as just described； is made to remove for the purpose of introducing the object to be copied； and upon it the prepared paper； the back is then replaced； and； by aid of the cross piece and screw； e。； the whole is brought into close contact with the glass。
The objects best delineated on these photographic papers； are lace； feathers； dried plants； particularly the ferns； sea…weeds and the light grasses； impressions of copper plate and wood engravings； particularly if they have considerable contrast of light and shade（these should be placed with the face downwards； having been previously prepared as hereafter directed） paintings on glass； etchings； &c。
To fix the Drawings。Mr。 Talbot recommends that the drawings should be dipped in salt and water； and in many instances this method will succeed； but at times it is equally unsuccessful。 Iodide of potassium； or； as it is frequently called； hydriodate of potash； dissolved in water； and very much diluted； （twenty…five grains to one ounce of water；） is a more useful preparation to wash the drawings with； it must be used very weak or it will not dissolve the unchanged muriate only； as is intended but the black oxide also； and the drawing be thereby spoiled。
But the most certain material to be used is the hyposulphite of soda。 One ounce of this salt should be dissolved in about a pint of distilled water。 Having previously washed the drawing in a little lukewarm water； which of itself removes a large portion of the muriate of silver which is to be got rid of； it should be dipped once or twice in the hyposulphite solution。 By this operation the muriate which lies upon the lighter parts will become so altered in its nature as to be unchanged by light； while the rest remains dark as before。
It will be evident from the nature of the process； that the lights and shadows of an object are reversed。 That which is originally opaque will intercept the light； and consequently those parts of the photogenic paper will be least influenced by light； while any part of the object which is transparent； by admitting the light through it； will suffer the effect to be greater or less in exact proportion to its degree of transparency。 The object wholly intercepting the light will show a white impression； in selecting； for example； a butterfly for an object； the insect； being more or less transparent； leaves a proportionate gradation of light and shade； the most opaque parts showing the whitest。 It may be said； therefore； that this is not natural； and in order to obtain a true pictureor； as it is termed； a positive picture we must place our first acquired photograph upon a second piece of photogenic paper。 Before we do this； however； we must render our photograph transparent； otherwise the opacity of the paper will mar our efforts。
To accomplish this object； the back of the paper containing the negative； or first acquired photograph； should be covered with white or virgin wax。 This may be done by scraping the wax upon the paper； and then； after placing it between two other pieces of paper； passing a heated iron over it。 The picture； being thus rendered transparent； should now be applied to a second piece of photogenic paper； and exposed； in the manner before directed； either to diffused day…light or to the direct rays of the sun。 The light will now penetrate the white parts； and the second photograph be the reverse of the first； or a true picture of the original。
Instead of wax； boiled linseed oilit must be the best and most transparent kindmay be used。 The back of the negative photograph should be smeared with the oil； and then placed between sheets of bibulous paper。 When dry the paper is highly transparent。
IV。 APPLICATION OF PHOTOGENIC DRAWING。This method of photogenic drawing may be applied to useful purposes； such as the copying of paintings on glass by the light thrown through them on the prepared paper Imitations of etchings； which may be accomplished by covering a piece of glass with a thick coat of white oil paint； when dry； with the point of a needle； lines or scratches are to be made through the white lead ground； so as to lay the glass bare； then place the glass upon a piece of prepared paper； and expose it to the light。 Of course every line will be represented beneath of a black color； and thus an imitation etching will be produced。 It is also applicable to the delineation of microscopic objects； architecture； seulpture； landscapes and external nature。
A novel application of this art has been recently suggested； which would doubtless prove useful in very many instances。 By rendering the wood used for engravings sensitive to light； impressions may be at once made thereon； without the aid of the artist's pencil。 The preparation of the wood is simply as follows：Place its face or smooth side downwards； in a plate containing twenty grains of common salt dissolved in an ounce of water； here let it remain for five minutes； take it out and dry it； then place it again face downwards in another plate containing sixty grains of nitrate of silver to an ounce of water； here let it rest one minute； when taken out and dried in the dark it will be fit for use； and will become； on exposure to the light； of a fine brown color。 Should it be required more sensitive； it must be immersed in each solution a second time； for a few seconds only。 It will now be very soon effected by a very diffused light。
This process may be useful to carvers and wood engravers not only to those who cut the fine objects of artistical design； but still more to those who cut patterns and blocks for lace； muslin； calico…printing； paper hangings； etc。； as by this means the errors； expense and time of the draughtsman may be wholly saved； and in a minute or two the most elaborate picture or design； or the most complicated machinery； be delineated with the utmost truth and clearness。
CHAP。 IX。
CALOTYPE AND CHRYSOTYPE。
The materials and apparatus necessary for the Calotype process are
Two or Three Shallow Dishes； for holding distilled water； iodide； potassium； &c。the same water never being used for two different operations。
White Bibulous Paper。
Photogenic CameraFig。 9。
Pressure FrameFig 29。
Paper； of the very best qualitydirections for the choice of which have been already given。
A Screen of Yellow Glass。
Camels' or Badgers' hair Brushes：A seperate one being kept for each wash and solution； and which should be thoroughly cleansed immediately after using in distilled water。 That used for the gallo…nitrate is soon destroyed； owing to the rapid decomposition of that preparation。
A Graduated Measure。
Three or Four Flat Boards； to which the paper may be fixed with drawing pins。
A Hot Water Drying Apparatus； for drying the paper will also be found useful。
In preparing the Calotype paper； it is necessary to be extremely careful； not only to prevent the daylight from impringing upon it； but also to exclude； if possible； the strong glare of the candle or lamp。 This may be effected by using a shade of yellow glass or gauze； which must be placed around the light。 Light passing through such a medium will scarcely affect the sensitive compounds； the yellow glass intercepting the chemical rays。
Preparation of the Iodized Paper。Dissolve one hundred grains of crystalized nitrate of silver in six ounces of distilled water； and having fixed the paper to one of the boards； brush it over with a soft brush on one side only with this solution； a mark being placed on that side whereby it may be known。 When nearly dry dip it into a solution of iodide of potassiu