Although this may seem a rather laborious practice, it is not so in reality, and so great is its educational power that I anticipate 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 assure 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.
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.