Photogravure Part 3

FORMULA FOR ACID BATHS.

(H. R. BLANEY.)

No. 1 should register to Beaume's scale 42 deg.

No. 2 " " " " " 37 deg.

No. 3 " " " " " 33 deg.

No. 4 " " " " " 30 deg.

The temperature of the bath to be at 63 deg. Fahr. when tested.

(DENISON'S.)

No. 1 should be made to register Beaume's scale, 45 deg., the percentage of perchloride in this solution is 47, and the specific gravity 1.444.

No. 2, 40 deg.; percentage, 41; spec. grav. 1.375 No. 3, 38 " " 38; " 1.339 No. 4, 35 " " 35; " 1.313 No. 5, 27 " " 27; " 1.225

From an article in the _Photographic News_ (English), Nov. 1, 1889, as practiced in India.

BITING BATH.

(WATERHOUSE.)

No. 1, sp. grav., 1.444; ap. per ct. of Fe_{2}, Cl_{6} = 47 No. 2, " 1.375; " " 41 No. 3, " 1.339; " " 38 No. 4, " 1.313; " " 35 No. 5, " 1.225; " " 27

A stronger solution of 48 deg. has been tried (by the above) but has no penetrating power through even the thinnest film.

ANOTHER FORMULA.

For large plates, 20 lbs. perchloride of iron and distilled water, until weight amounts to 1.500 grammes per 1000 c.c. From this four (4) solutions are made, at

No. 1, 42 deg. Beaume; spec. grav. 1.420 No. 2, 38 " " " 1.375 No. 3, 35 " " " 1.330 No. 4, 31 " " " 1.285

The plate is now ready for biting. Keep a record of the bitings, and length of time for each one, for after-study; also note the time of exposure of the tissue, age of same, etc., etc.

Pour the acid from a gla.s.s graduate with one sweep over the plate, removing all bubbles with a feather, noting the time of immersion so as to guide you. Start with 42 deg., having ready the 37 deg. in another graduate, watch carefully the action of the acid, and if the resist has been properly printed, the action of the acid will show after a minute; if longer it means a generally longer biting for each bath.

AVERAGE BITINGS.

42 deg., No. 1 5 minutes 37 deg., No. 2 5 minutes 33 deg., No. 3 2 minutes 30 deg., No. 4 2 minutes

Temperature of bath at 70 deg. Fahr., with No. 103 tissue.

Total of different bitings, from 10 to 25 minutes, according to depth of printing. It always varies. There is no hard and fast rule; you must in time learn to judge by your eye alone. The acid will first attack the thinnest part of the film, wherever that may be, and when the darkening of the copper ceases to spread to the next thickest parts, instantly pour off the acid, and pour on the 37 deg. Do not allow the atmosphere to act on the gelatine while biting any longer than is necessary to pour off one bath and quickly pour on a new one. The 37 and 33 deg. baths are for the middle tones, the 30 deg. for the most delicate ones. The action of each bath is c.u.mulative, the 37 deg. biting a little where the 42 deg. had bitten, the 33 deg. doing the same for those before it, besides taking care of itself, and the 30 deg. attacking all more or less.

During the biting with the 30 deg. solution, it should be continued until the whites just turn color, and a minute beyond; that is, the copper should begin to show a very little under the thickest and darkest film.

(Note that in the carbon resist the shadows are transparent and the high lights are opaque.)

The length of the last biting very seldom is over two minutes. It is better to overbite your darks, and underbite your lights, if you vary any.

The amount of moisture in the air and the heat of the day influences the length of biting. In hot weather in summer it is very difficult to work the process, the walling wax being discarded and the copper (back and edges protected by varnish) placed in a porcelain tray, surrounded by ice-water and kept at 65 to 70 deg., and the acid pured over the plate to the depth of one inch.

[Ill.u.s.tration]

CHAPTER VII.

CLEANING AND POLIs.h.i.+NG THE PLATE, WITH TOOLS NECESSARY FOR RETOUCHING.

When the biting is finished rapidly place the plate under the tap and rinse thoroughly, breaking away the film with your fingers; it seems to have rotted under the action of the acid and is easily removed.

Remove the walling wax, clean off the varnish with chloroform or turpentine, or alcohol first, and chloroform last. This leaves a dim picture on the plate, with a kind of sc.u.m over it; wet the plate with turpentine and start heavily with rouge, rubbing to and fro equally all over the plate with a ball of absorbent cotton; continue this treatment, using less and less rouge and more turpentine until you give the final polish to the high lights with a clean dry piece of cotton. Be very careful not to overdo in rouging; the sc.u.m (if the biting of the plate is of medium strength) should clear from the plate with hardly a touch, and with very little rouging. Some plates require a great deal of rouging; it then generally means that you must look to your sensitizer.

I again draw your attention to the rouging; here is where any artistic feeling you may possess will come into play with taste and patience.

After the plate is rouged sufficiently, an engraver's burnisher is used to clean up the highest lights and to modify others. Two or three roulettes of different fineness are valuable to touch up any darks that need deepening; it matches very well with the grain, but I am always trying to dispense with the use of the roulettes; one ought to get it with the acid alone. A No. 6 sewing needle in a holder (dentist's pin-holder, screw end) is necessary to touch out occasional white specks. You will have plenty of them at first unless you look out carefully for dust on the film; keep all your solutions constantly attended to by occasional filtering, and don't use your sensitizing solution more than half a dozen times; keep it well corked; if it gets old it sc.u.ms the plate too much.

[Ill.u.s.tration]

CHAPTER VIII.

PRINTING THE PLATE AND STEEL FACING.

Before final finis.h.i.+ng by hand a working proof should be printed from the plate by an expert plate printer, by which, what the plate needs can be determined before final proving.

Have the plate proved on different papers, and with different colored inks, so as to judge the effect. Imperial j.a.pan is the best paper, besides etching paper, India, thin Chinese and j.a.panese papers. The cost of proving per single proof is 25 cents for a 4 6 plate on Imp. j.a.pan, about $2.00 per doz. same paper; etching paper, about $5.00 per 100--less for large quant.i.ties.

A second-hand D press, suitable for printing large or small editions or for proving, can be bought in Boston or New York for from $75 to $100.

For instructions in printing see Hamerton's "Etchers and Etching."

STEEL FACING.

The life of a photogravure plate without steel facing does not last much beyond 75 impressions, so that if an edition is needed, send the plate to any good printer who will have it steel-faced for you; their charges are very moderate, about 50 cents for a 4 6 plate. The steel-facing is accomplished by first making the plate chemically clean, as before preparation for graining, only be very thorough in using an old tooth-brush to get out the dirt and in addition use chloroform before using potash. Then solder a copper wire on to the back. The negative wire is attached to the copper plate. To the positive pole of the quart Smee battery is fastened a bright steel plate same size of copper, in a gallon jar. The plates are hung from gla.s.s rods 1/2 inch apart, a sufficient quant.i.ty of the following solution to be poured into the jar:

(DENISON'S.)

Warm water 20 ounces Ammonium chloride 3 ounces Sulphate of iron and ammonia 4 ounces

Filter, and let stand for 24 hours. Five (5) minutes will cover the plate with a thin film of steel.