The Barnet Book of Photography Part 18

If an enamelled iron dish be employed, these precautions are not so necessary, though they may still be used with advantage.

Next we shall require another dish or similar vessel into which we pour a weak solution of hydrochloric acid, the usual proportions being:--

Water 70 parts Pure hydrochloric acid 1 part

This const.i.tutes the whole of the very simple apparatus needed, and we may now proceed to develop our print, which as already described is exposed to light in a printing frame in the usual manner until the image appears rather less than half-printed.

DEVELOPMENT OF THE PRINT.

If convenient it would be an advantage to have the above-mentioned apparatus set up close to the window or other situation where the printing is actually carried on in order that each print may be developed and finished off forthwith,; the reason for this will, I think, appear as we proceed.

Development--that is, the changing of the print from the partially visible condition to its full degree of intensity--is practically instantaneous. The image does not gradually attain its maximum strength as in a negative or bromide print, but does so within a few seconds of its coming into contact with the oxalate of potash solution.

[Ill.u.s.tration: Fig. 1.]

Having put into the dish on the tripod stand sufficient of the saturated solution of oxalate of potash to cover the bottom of the dish to the depth of half an inch or an inch, we light the lamp or stove and bring the solution up to a temperature of about 70 Fahrenheit. This may be tested with a thermometer or may very well be guessed by touch; we merely require the solution quite warm, but not so hot as to cause the slightest inconvenience if the fingers are placed therein. This will be a sufficiently accurate guide as to temperature.

In case any dust or sc.u.m should have acc.u.mulated on the surface of the bath, wipe the surface of the solution with a piece of clean paper, and now take the first print to be developed in both hands, giving it a decided curl, or roll it round into a cylinder _sensitive side out_, so that it naturally takes a curled-up form (Fig. 1). We now take the print to the dish containing the oxalate solution without previous washing and without exposing the paper to the influence of light or moisture, and lowering the edge of the paper held in the left hand, sensitive side downwards, until it touches the fluid quickly and smoothly bring the rest of the print down until the right-hand end finally reaches the solution, then give it a sliding sort of shake in order to set free any bubbles of air which may be imprisoned under the paper, and then on raising the paper again after five to ten seconds, the image will be found to have come out to the full degree of visibility, which the amount of exposure had paved the way for.

The paper may be returned to the oxalate bath for a minute or two longer if it be thought desirable, though only in the case of a very cold bath is any effect produced on the print by the oxalate after the first few seconds. The print is then pa.s.sed _direct_ to the hydrochloric acid bath, which should be ready in a dish close at hand, and the print is now practically finished.

Before placing the print in the acid bath it may be noticed that the portions of the print not affected by light still remain yellow, and this yellowness the acid bath removes almost at once.

In order to effectually remove the yellow surface (which is the unacted-upon sensitive salts and hence upon their removal the permanence of the print depends) three successive applications of the acid bath should be resorted to, the prints remaining for 5 to 10 minutes in each, and then finally washed in running water for a quarter-of-an-hour, dried between blotting paper or in any other manner preferred, and the platinotype print is finished and ready for mounting.

It should be seen from the foregoing general outline of the process that for directness, simplicity, and for the short time in which a finished print may be produced that platinotype stands alone amongst printing methods.

There are, however, some points needing careful consideration at each stage of the print's production, and to these we may now pay attention.

PRACTICAL CONSIDERATIONS AS REGARDS EXPOSURE.

As has already been stated right exposure const.i.tutes the crux of the whole process; this once mastered the rest of the performance--development, clearing in acid and washing--is so simple that the chance of failure is remote.

Hence the greater need of paying especial attention to the question of exposure or printing.

Obviously, the duration of time of exposure cannot be fixed, not even to the extent it can be in bromide printing or any other method of printing with artificial light which may be a definite and permanent quant.i.ty.

The variable quality of the daylight and the density of the negative are both fluctuating factors in the calculation and hence some means may advisedly be resorted to for acquiring a sort of exposure index suitable for each individual negative and every variety of light.

First let it be noted that even with very great over-exposure the image will not become wholly visible, whilst to the inexperienced eye but little change takes place in the appearance of the printed image after the correct exposure has been reached.

If then the print has been over-exposed, the fact is not made evident until the print is subjected to the influence of the oxalate developing bath.

To start platinotype work trusting to chance or good fortune to secure for us good results, means that our whole course will be one of uncertainty and filled with exasperating disappointments to say nothing of the amount of paper and material which is certain to be wasted in unsuccessful efforts.

The reader will probably have learned something of this from his past experiences of negative exposure, the difficulties of which he has by now, we may hope, overcome by careful and patient study, or else if he is not even now undergoing this stage of learning he is the victim of endless mistakes, every plate exposed is a shot in the dark with no certainty attending any one of them.

Exposure, however, in platinotype is not so difficult a matter as that of a dry plate, and the correct exposure with any particular negative once ascertained, every subsequent print from the same negative can, by simple mechanical means, be made with the certainty of its being _an exact facsimile_ of the others.

PRINTING WITH AN ACTINOMETER.

Several kinds of Actinometers are made for sale, the purpose of which is either to indicate the right exposure of a plate in the camera or to tell the duration of exposure for papers such as platinotype or carbon, the image on which is invisible, or nearly so.

A simple, yet thoroughly efficient meter may be made as follows:--Cut some fine tissue paper or _papier mineral_ into strips about a quarter of an inch wide and attach one to a piece of clean gla.s.s 4-1/4 3-1/4 with fresh starch or other colourless mountant.

Upon this first strip and exactly over it place a second, but bring it to within a quarter of an inch of the end of the first, next place a third strip in like manner a quarter of an inch short of the second strip, and so on until some seven or eight strips have been fixed. The combination will now be somewhat as the following drawing (Fig. 2), thus forming a tissue band which at each quarter-inch is one thickness more opaque.

[Ill.u.s.tration: Fig. 2.]

In the centre of each strip or increased thickness, paint with opaque colour, black or red, a letter or figure as in (Fig. 3). On the back or other side of the gla.s.s to which these strips are attached, paint over or cover with opaque paper all except the s.p.a.ce covered by the strips. Now place the whole in an ordinary 1/4-plate printing frame, with the paper strips inside, next adjust a piece of silver paper, alb.u.menized, or gelatine chloride precisely as though printing from a negative. Close the back and we then have a thoroughly efficient actinometer.

[Ill.u.s.tration: Fig. 3.]

We now put out our first piece of platinotype paper to print, and alongside it so as to receive the exact same amount of light, we place our actinometer.

The first print must admittedly be guess-work.

After an interval of time, which may vary from say fifteen minutes to an hour according to the amount of light, we will withdraw the frame containing the platinotype print, and _simultaneously turn the actinometer over with its face down_, thus stopping its printing whilst examining the platinotype.

Retiring from the light we examine the progress of printing precisely as in silver printing, and we shall probably find that the image on the negative is now faintly visible on the platinotype paper, impressed in a sort of warm grey colour.

If the darkest portions are of about the tint which we might produce by shading with an H pencil on a piece of primrose yellow or pale buff paper, we may reckon that the print has been sufficiently exposed.

Now refer to the actinometer and see what has taken place on the silver paper which we put into it. Probably while the platinotype paper has been reaching the required depth of printing, the silver paper has also registered the image of the strips of paper, and has become printed through up to the fourth or fifth step of the tissue strips, showing on each strip its letter in white. Make a note of the highest letter visible and proceed to develop the platinotype print. If upon development the print is weak and grey, lacking depth or intensity in the deepest shadows, and having blank and detailless whites for the higher tones, we may reckon that our print is under-exposed. The letter visible then, _with that particular negative_ is not sufficient. We then shift the paper in the actinometer so as to get a fresh portion under the tissue strips, or we subst.i.tute a new piece. We refill the printing frame and print again until the actinometer registers one, two, or three more steps and letters, and then try again. If, however, in the first case the platinotype print upon development gives a heavy dark print, with the details in shadows blocked up, and the high-lights grey, the whole possessing an overdone appearance, then in our second attempt we shall stop printing when the actinometer records some one or two letters less. But we may be more fortunate in our first attempt, and the print may be about right. In that case we mark on that negative in some way the tint or step or letter in the actinometer at which we arrested action, and henceforth, no matter the time of year, hour of the day, or lat.i.tude, that negative will give a similar print if stopped in accordance with that memorandum which it bears.

If, however, we do not hit the right exposure the first time, we are pretty certain to do so the second, or at the most the third time, and having done so, we have not only an infallible guide for all subsequent prints from that same negative, but we have also some sort of index to base our calculations on for other negatives. Thus if we at once proceed to print from another negative, that is, before any considerable alteration takes place in the light, we may by comparing the negatives at least estimate what will probably be the second negative's printing letter or step on the actinometer.

Sooner or later every negative (especially those from which we antic.i.p.ate wanting subsequent prints) should bear either on the negative itself, or else in a carefully kept register or note book its correct printing letter.

Although this may seem a rather laborious practice, it is not so in reality, and so great is its educational power that I antic.i.p.ate that after the first dozen or so negatives we shall almost dispense with the actinometer altogether, having by then trained the eye to tell when a print is finished merely by the appearance of the half-visible image. Do not let this prospect, however, tempt the beginner to dispense with this valuable help at first, for to the inexperienced eye the appearance of the platinotype image is very deceptive, and having under-exposed the first print, it will not be safe to judge the extra printing of the next print only by the eye; the beginner is nearly certain to err, and the eye must not be trusted until it has had considerable training.

After having had some considerable and varied experience in platinotype printing, one feels no little regret that an operation which has become so simple cannot be laid before a beginner in a more precise and definite manner, and I can only a.s.sure my reader that in a very little while what may now look like a very serious business, only surmountable by long and serious practice, will become a sort of intuitive faculty, and just as one feels after a little practice the precise amount of pressure which one should use when the fingers are placed on the notes of the piano, so just the right _visible_ depth of print required to give a developed print of such and such intensity comes to be a matter of instinct.

It may here be stated that paper which has been affected by damp gives a slightly less visible image than dry paper. But moisture alone without oxalate will effect partial development, and if the time of exposure to light be so greatly prolonged, that despite all precautions moisture obtains access to the print during exposure, this may, as it were, start a kind of local development whilst the paper is still in the frame and printing, so that on looking at the print to watch its progress some of the deeper shadows may have sprung quite suddenly into a deep blackish-grey colour. In many cases this will quite spoil the finished result, whilst in others no harm seems to be done when the print is ultimately developed.

Remembering that the high-lights and indeed some of the lighter tints of the print are quite invisible until after development, care should be taken to look at the paper only in decidedly subdued light, or better still, artificial light, because the injury which is being done by even a short exposure to actinic light is not made manifest until after development, and as most of us know how soon a piece of silver paper will discolour in even moderately faint daylight, we should be additionally cautious with platinotype paper which is from twice to three times as sensitive to light.

[Ill.u.s.tration: Fig. 4.]

SOME POINTS TO BE CONSIDERED WITH REGARD TO DEVELOPMENT.

To avoid confusion it will be well to repeat here that at present we are only considering the practice of what is known as the cold-bath paper. This term is applied only in a comparative sense. The older hot-bath process requires the developing bath to be raised to a temperature of about 170 F., whereas the best temperature for the cold process is about 70 F. or even less; nevertheless, the cold-bath paper _may_ be developed in an oxalate bath of 170 or even hotter, so also it may be developed on a solution which is quite cold. The result of altering the temperature is two-fold and may be stated thus:--_The colder the bath_, the _colder_ the colour, that is, the _bluer_ the greys and blacks, also development is slower and takes longer, and the contrasts harder. _The hotter the bath_ the warmer or browner the colour of the print; the more sudden the development and the greater the amount of half-tone and consequent softer contrasts.

With these maxims in mind some amount of control may be exercised over the prints produced, especially as regards arresting development at any point desired if a cold developer be used, but in such case the print must be instantly removed to and plunged into the acid bath, until which immersion development continues, even after the print has been removed from the bath.

Development, as a general rule, should be conducted in feeble daylight or artificial light.