DEFECTS IN PRINTS, AND REMEDIES.
It must be understood that chloride of gold is usually somewhat acid, and that borax, bicarbonate of soda, or whatever is used with it is intended to neutralise this acidity and, moreover, to render the solution slightly alkaline. If the bath refuse to tone, the test papers must be used to find out whether it is alkaline or not. If red litmus papers be placed in an alkaline solution its colour is changed to blue. A book of test paper slips should be purchased, and a little piece of red litmus should be placed in the toning solution. If no change of colour takes place in the paper after a minute or so we may assume that the solution is either acid or neutral. In either case we have to acid some more of the salt which was mixed with the chloride of gold to constitute the toning-bath. We may add a little at a time till the red litmus shows signs of changing its colour. If we add so much that the red colour of the paper is changed to blue the moment it is placed in the solution, we have rendered it too alkaline.
If the bath adopted be one which has to be kept for some time before it is used we must notice that the gold has not deposited itself at the bottom and on the sides of the bottle as we described already. The stock gold solution without any alkaline reaction is generally very stable, but we have known cases in which the gold has thrown itself down. Of course when the gold has become deposited in the bottom of the vessel we have not far to go to seek for the cause of the refusal of the bath to tone.
If the toning solution be very cold, toning may take a long time, or the prints may even refuse to tone at all. In winter time the temperature of the bath may be raised somewhat, but never above 70° or 80° Fahr.
Some papers, without being in any way defective, require a toning-bath of greater strength than the one we have given. If we find that prints take too long to tone, and at the same time we are sure that our bath is not faulty, we may strengthen it by adding gold and whatever other chemical we are The bath may be made even double as strong as we have described.
The Prints tone sufficiently well, but the greater part of the Tone is lost in the Fixing-Bath and does not return.
Before entering on particulars of this fault we should say that all photographers are not agreed as to the necessity of giving to the prints before they are toned the thorough washing that we have described. There is no doubt that if but a slight washing be given, the process being stopped whilst the water which runs from the prints is still cloudy, indicating that. considerable silver nitrate remains still in the paper, toning will go on much more rapidly. It is our experience, however, that the tone thus readily gained with only partially washed prints is very liable to be lost, or at least to deterior ate in the fixing-bath. We have, moreover, reason to believe that prints toned whilst there is still considerable free silver nitrate in the paper are less permanent than those toned after thorough washing. The greater number of photographers prefer to wash their prints thoroughly before toning them.
Another cause of loss of tone in the fixing-bath is the use of too strong a solution of hyposulphite of soda. The fixing solution for plates may be made up by guess after a little experience, but weighing should always be resorted to for the print-fixing solution. Some recom mend for prints the use of a fixing-bath containing five ounces of hyposulphite of soda to each pint of solution. This we consider far too strong.
The Prints tone unevenly.
The most common cause of this defect is to be found in the sticking together of prints through insufficient motion during toning, and especially if a solution so strong as to bring about the change of colour in a few minutes be used. The prints should be kept in co-nsta-nt motion till they are all toned.
Finger-marks on the albumenised side of the paper are liable to come out as untoned marks in the print.