ITS C 0 lI P 0 U ?; 1)S

color-photography, This work was begun nearly two years ago by Messrs. Frary and Baker, and was contintied during t.he past year by llessrs. Frary and...
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T H E D I R E C T PRODUCTION O F POSITII'ES I S THE C=lllERA1B T ,IIEA\SS OF THIOLTRE;l -1SD ITS C 0lIP 0U ?;1)S E;Y F R A S C I S C. F R A R T , RALPH XT. 1IITCHELL A S D R1.SSEI.L

E.

B.\KER

The increasing use of transparent positives in photographic processes inspired us to begin the study of methods for their direct production in the camera. I t was hoped t h a t such a process could be developed as would make i t possible t o produce lantern-slides, transparencies, and positives for use in the Askau process, without first making negatives. I t was also hoped t h a t the process would enable us to shorten the maniptilation in the Lumiere rlutochrome and similar processes in color-photography, This work was begun nearly two years ago by Messrs. Frary and Baker, and was contintied during t.he past year by llessrs. Frary and Mitchell. Ivaterhouse' first described the use of thiourea in the direct production of positives, and recommended the use of the double salt, tetra-thiourea-ammonium bromide. His n-ork seems t o ha\-e attracted little attention. however, arid apparently the results obtained with thiourea by others" were unsatisfactory. Recently Perley' has ivorked on this method. apparently obtaining more satisfactory results, using a hydrochinon developer instead of the eikonogen de\-eloper recommended by Waterhouse. B u t his directions are not very explicit, all his n-ork was done on lantern-slide plates, which are quite different from ordinary plates, and we found t h a t attempts to make positives according to his di-

' -4 paper read before the Eighth International Congress of -1pplied Chemistry in S e w T o r k , September, 1 9 1 2 . Eder: Jahrbuch fur Photographie, 16, I;O (1892). Nipher: Trans. Acad. Sei. St. Louis, I O , 2x0 (1900). (Juoted in Jour. Phys. Chem., 13, 23; (1909). Jour. Phys. Chem., 13,649 (1909).

rections were seldom successful, and then only to a limited extent. %'orking according to his directions, and using ordinary plates, we found i t \-cry hard to get results a t all concordant, when all the conditions appeared to be the same. Using thiourea as he recommended lye obtained fair positives, fogged plates, and hybrids, a l l under the same conditions of exposure, strength of developer, and time of development. I t appeared that there as another factor capable of exercising a great influence, and this \ v a b fotind to be the temperatiire o f the de,: e 1oper . i i 7 e h a ~ iiiatle e :iboLit Ooo plates i i i all by this process. anti find that the pretioniiiiaitt factors in the control of the result.: are : I I brand oi plate, -7 1 proportion of thiourea or its salts. ( 3 : developiiig agent, 71) propcirtioii of alkali, i proportioit of restrainer. i h character of thiourea salt used, i 7 I teniperatiire of t1e~;eloper. I h I method of applying the thiourea c o n p o ~ ~ i i d For . uniformity, most of our plate; ha\-e been made by printing under a lantern-slide a t ;I distance of I ' met.er.; from it standard candle, the apparatus being set up iu the dark room, and the candle thoroughly protected from d.raughts of air. 11-e fiitd that the de; eloper ivhich gi\.es the best results depends quite larqely oii the brand oi plate used. This is not ~vholly a matter of the relati\-e speed of the difIererit plates. b u t seems to depend 011 the composition of the emulsion. Eest results are obtained u-ith plates of only moderate speed. such as the Cranier Banner S or the Seed 26. Most of our \vork has been doiie on the Cratner Banner S plate; after working out the effect of 1-ariations of the conditions on this plate, other plates \vere used for comparison. i f ' e have used Seed 2 6 , 2 ; . 3 0 , process, and lantern-slide plates, \.ulcan plates, Lumiilre Blue Label, and LumiPre Sigma plates. In some cases the developer had to be modified to get the best res u 1t s . When the thiourea was used as a separate bath before 1

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del-elopment, as recommended by Perley, it was used in a I : IOOO solution. Ti'hen mixed with the del-eloper. the same strength n-as used, in proportions \-arying from 30 to 40 parts per 100 parts of developer. Equal parts of the t\\-o solutions seem to gi1.e the best results: less thiourea has too great a teiirlency t o give hybrids. ;ind more produces escessil-e fog. \ire find that difi'erent de\.eloping agents Iia~,-edifierelit efiects. The hydrochinoii formiila rccommentlcd by Perley : \rater 100, sodium sulphite idryi 1 2 . 0 , hydrochinoil 601.' - 7 . 1 g n i , ; Sol. B : lvater roo, sodium carbonate' ( d r y ' 2 5 . 2 g m . , \\-as the one \i-hich seemed to Ivork best, and \\-as used in most of the experiments. Satisfactory positi\-es \Yere also obtained with an adiirol de\-eloper containing a rat her large amount of alkali, but dianol and amidol \\-ere unsatisfactory. The effect of inetol is Yery peculiar. -1 small amount of it added to the regular hydrochinoii de\-eloper increases very much the density of the negatil-e image \\-hich del-elops first, but acts as restrainer for the positix-e image. Hybrids generally result, although by decreasing the exposure very much and developing for a \.cry short time, some rather poor positives could be obtained. I n general. the more alkaline the developer. the stronger the positive and the lveaker the negative image obtained. 'The effect of the thiourea compounds seems to he dependent ',-cry largely on the presence of a large amount of alkali. \i7ith some plates (Seed Process, I,umii.re Blue Label, and I-ulcani the amount of carbonate in the developer above mentioned, which was excellent for the Cramer Eanner S , must be considerably increased to get the best results. \i7ith Seed Lantern Slide Plates, the best fesults were obtained by reducing the sulphite and diluting the developer. \Vith adurol the amount of carbonate required was four times that recommended by the manufacturers for development of the negative, or more than t h a t required for the regular hydro-

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Mr. Pcrley has since informed me that this should be t h r crl-stallinc salt, \vc understood from his paper i t was the anhydrous salt, and so used that

F . C. Frary, R . ItT. i2litchell and R. E . Baker

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chinon developer. Less than the proper amopnt of carbonate in a n y developer produces hybrids; more produces brown fog. T h e color of the resulting image is also dependent on the amount of carbonate in the developer, as well as the amount of sulphite, the developing agent. temperature, time of development, and brand of plate. One strange thing about the process is the relatively large amounts of potassium bromide t h a t are required t o produce any restraining efTect on the developer. It requires cubic centimeters rrhere one ir-ould use drops in the ordinary development. -As much as 7 cc of a I O percent solution has been used in 100 cc of the mixed developer ( I part I part E , 2 parts thiourea solution), the only effect apparent being increased time required for development. If thiourea be used the addition of some bromide is adyantageous, and the same is true of tetra-thiourea-ammonium bromide, b u t tetrathiourea-ammonium chloride seems to work better Jvithout a n y restrainer. -Acetone sulphite n-as a vigorous restrainer, b u t seemed to hold back the half-tones more than the shadolvs, tending to $1-e harsh results. Potassium iodide was a very much more powerful restrainer than the bromide ; the latter being easier to control was generally used when a restrainer \vas necessary. The tetra-thiourea-ammonium bromide, recommended by IYaterhouse, b u t apparently not tried by Perley or other investigators, n-as \-ery much superior to the simple thiourea, giving clearer and better positives. Most of the work was done with i t . The corresponding chloride salt, however, appears to be better still, and works without a restrainer. The iodide was not very satisfactory. -111 these salts were prepared according to the directions of Reynolds. ' IT-e would prefer the chloride, as far as our experience goes, although the bromide is a great improvement on the plain thiourea. One of the most important factors in the process is the temperature of t h e developer, and this appears never t o have ~

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Jour. Chem. SOC.,59, 384 (1891).

Positives in the Camera by Thiourea, Etc.

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been noticed b y any one. Control of all the other factors failed t o give us reproducible results until the temperature was considered. For the method recommended b y Perley {bathing in thiourea solution, with subsequent development) t h e best results were obtained a t about 2 4 O , much lon-er temperatures (18 to zoo C) giving hybrids, while higher temperatures (28 t o 29') gave very strong positives, 11-ith a heavy bron-n fog. This fog was troublesome a t all times with this separate-bath process, unless the temperature was so low t h a t the negati\ye image came up so strongly as to make the result a hybrid In the use of the thiourea or its compounds in the developer, as we prefer, the temperature may 7.ar-y from 1 2 to z o o C. b u t temperatures of I j to 18' C ( 6 0 to 6j0F)seem t o gi\-e the best results. Higher temperatures result in rapid development, with production of fog; lon temperatures decrease the speed of development, and temperatures especially the development of the positive A%t a5 low as ;" C the negative image could be developed, b u t no positive image \vas obtained below about I I O This effect of temperature seems to be independent of the effect of all the other variables A4.s indicated aboye, \le find t h a t we obtain much better results b y mixing the solution of the thiourea compound with the developer i i i the proportion of I I than by usinq i t as a separate b a t h . I n the latter case more trouble is found with fog, the results are more irregular. and tend to be spotted, the time of development and the difficulty of control are increased Using the tn-o solutions together, development is niuch t h e same as in the ordinary process, except t h a t i t takes less time. The following procedure is recommended for the development of positives on the Cramer Banner X plate: The exposure is made in the ordinary x a y ! and should be a little longer than for the production of a negative. Double the normal exposure will usually be about right. The hydrochinon developer recommended on a previous page is used,

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F.C. F r a i j , , R . I T - . .\Iitchell m i d R. E . Baker

mixing one p a r t of A, one part of E , and two parts of a I : 1000 solution of either thiourea, tetra-thiourea-ammonium bromide or tetra-thiourea-ammonium chloride, preferably the latter, If thiourea is used, 0.5 cc of I O per cent potassium bromide are added per I O O cc developer; if the ammonium bromide compoLiiid be used, 2 c'c of the bromide solution per IOO cc developer, while if the animonium-chior-ide compound is used no restrainer is needed. Develop as ~ i s ~ i akeeping l, temperature of developer betn-een r g and 18' C; the negative image first appears, then t h e plate appears to fog, and soon the positil-e image can be seen by transmitted light. Care must be taken not to overdevelop, as the positive image irill be quite strong. Rinse, fix, and \\-ash as usual. If the negative image is too strong, i t indicates over-exposure; the plate may be reduced slightly with the Farmer reducer. . I foggy positix-e. i\-ith practically no negative indicates under-exposure. if the temperature of the developer has been kept Jvithin the proper limits. Development is rapid, being usually complete within four minutes. The positive image is characterized b y its color; with the above conditions it will be red, warm sepia, or purplish red. The negative image is black and very transparent. For making lantern-slides. the exposure Ivill, in general, be less than t h a t required to make a negati;-e under the same conditions, and the developer should be diluted n-ith a n equal s-olume of water. If, however, the subject to be reproduced be a line-drawing, ftill strength developer and normal exposure may be used, followed b y slight reduction. This will give excellent contrast. In fact, the principal fault of the process from the viewpoint of the slide-maker is the large amount of contrast obtained; the range from high-light to shadow is as great as in a good negative, consequently the slides of scenes tend t o be too heavy in the shadows. This defect is minimized if a n ordinary plate is used instead of a lantern-slide plate. Excellent positives have been obtained on films from a n Eastman Film-pack. They were made with the regular

Posztizes

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t h e Ca7ne.l.a bj' T h i o u r e a , Etc.

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developer, using the tetra-thiourea-ammonium chloride. The gradation and density thus obtained were excellent, and the films would make good lantern-slides. For Cramer Crown, Seed 26 and 2 ; plates the procedure recommended for the Crarner Banner X plate is satisfactory. For Seed process plates. 4 g anhydrous sodium carbonate should be added to each I j o cc of the normal de\-eloper abo\-e recommended, and for LumiPre Blue Plates, (> g carboiiate per I j(>cc tie\-eloper. The latter brand of plate did not $\-e tic. \-cry satisfactory positives LiiIder any circumstaiices : \ye are inclined t o belie\-e that the lot ivliich \ y e t kept too long lieiore Ive obtaiiied them. The process \i.orks \vel1 \\.itIi the I,umii.re .4utochrome plate, using the iiorma.1dei-eloper tlillited lvith an eqtial a1noLillt oi ivater. litit the strong red color of the image spoils the c-o!or rcnderiiig, so until this color can lie tnodified the process doe.: n o t seem to be applicable to thii plate. 111 the earlier part oi o ~ i r\\-ark, rather remarkable restilts \\-ere obtained \\it11 these plates, by bathitig them for one minute in I : r o o o thiourea solution before developiiig. and usiiig the regLilar meto:iuinone de:-eloper and reT-ersing solution recommended by the nianiifactiirers Results obtained indicated that sood plates could lie ob&necl Ivith aborit ' / i of the exposlire other\vise necessary. These p1at.e~w r e made in the laboratory. the strength of the light being controlled b y o\)ser\-atioii.; ivith the V'atkiiis Eee Meter. HoIvex-er. recent attempts to duplicate these results on short exposures out-of-doors ha\.e heen unsuccessful.

S u m m a r y and Conclusions The conditions for successfully carrying out the \\7aterhouse process of producing positives have been carefully studied and are given in detail. The most important of these is the temperature of the del-eloper. The double salts formed by thiourea with ammonium bromide and chloride work better than the thiourea itself, The amount of restrainer used varies n-ith the salt used.

F . C . Frary, R.W . Mitchell and R. E . Baker

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The character of t h e developing agent and the quantity of alkali in the developer play an important part in the process ; a strongly alkaline hydrochinon developer is recommended and the thiourea solution should be mixed with this as needed for use. The process gives positives of excellent detail, with about t h e gradation and density of a first-class negative. The exposure is relatively short, being about double t h a t required for the production of a normal negative. L

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