The Barnet Book of Photography Part 17

_Double Toning_, _i.e._, the print shewing different colours, points to insufficient washing or uneven action of the toning bath, _i.e._, not keeping the prints moving, or too slow toning, or that the toning bath does not suit the brand of paper.

_Blisters_ are usually due either to using a hypo fixing bath too strong, or pa.s.sing the print from one solution to another of a markedly different temperature. Hence the importance of dissolving the hypo either in tepid water or some time before use. The best all-round temperature for working this process is between the limits of 60 and 65 F.

_Tinting P.O.P._--The colours to be used may be the usual moist water colours by some good maker, or solutions of aniline colours.

These latter may usually be dissolved in water and applied in thin washes. The surface of the print should be rubbed as little as possible. If water colours are to be used it will be found helpful to prepare the surface of the print with one or other of the following preparations.

29. White (bleached) lac. 1 part Alcohol 12--15 parts

Apply evenly and quickly with a spray diffuser or with a broad soft brush, and let the print become _nearly_ dry before applying the colours.

30. The white of an egg in twenty ounces of water. Shake well, then add ammonia drop by drop until the mixture just very faintly smells of it. Filter and brush over the surface of the print. In mixing the water colours also use this alb.u.men solution in place of water.

_Advantages of P.O.P._--As compared with ordinary alb.u.menized silver paper the P.O.P. cla.s.s has the advantage of giving more detail with marked transparency in the shadows. The operations are more flexible and the results are as permanent, if not more so, than those on alb.u.men paper. The paper keeps in good condition for a longer time.

The negative giving the best results with P.O.P. is one having delicacy rather than vigour, _i.e._, a long scale of gradation of delicate steps is well rendered. Printing takes place quicker with P.O.P. than with alb.u.men papers. The cost of paper and materials is much about the same in both instances.

_Notes._--In the glazed variety of paper the smooth shiny surface is the sensitive one, and, of course, goes next the negative in the printing frame. In the matt paper the sensitive side may generally be known by its tendency to curl inward, _i.e._, the concave or hollow side is the printing side.

Formalin may be used in place of alum for hardening the gelatine. Of the usual 40 per cent. solution of formalin take one ounce and dilute with ten or twelve ounces of water.

Dark spots or specks are frequently due to metallic dust either from the fingers or in the water. Mounts having sham gold edges or bronze powders should be banished from the dark-room. Dry "pyro" floating in the air may also account for spots.

_Rev. F. C. Lambert, M.A._

[Ill.u.s.tration: UNLOADING. A. M. MORRISON.]

_Platinotype Printing._

[Ill.u.s.tration]

Amongst the various printing processes in common use amongst photographers, platinotype is unique in several respects.

Printing is conducted by daylight in precisely the same manner as silver printing, but the action of light only suffices to make the image partially visible. In this respect, platinotype stands, as it were, midway between what are familiarly termed "print-out"

processes--that is, those in which the image is made completely visible by daylight, and those in which the action of light is latent or invisible, such as bromide paper and in the carbon process.

The distinctive character of the platinotype print, with which, probably, everyone is so familiar that a platinotype effect almost amounts to a generic term, is not so much essential to the process, but has been largely determined by the different kind of papers and the preparation of those adopted by the manufacturers of platinotype printing papers.

In the first place, the platinotype print is before anything a matt surface print, and possesses a certain kind of texture or surface which gives the finished print an appearance similar to a pencil drawing or an engraving; an appearance largely a.s.sisted by the characteristic colour of the platinum image, which is black.

The invention and production of platinotype paper is due to Mr.

Willis and the Platinotype Company, and although subsequently there have been both English and foreign imitators, we may safely confine our attention to those papers made and supplied by the Platinotype Company.

As, however, the purpose of this article is to furnish the beginner with simple working instructions, rather than to describe the principles of the process, we will at once proceed to say how a platinotype print is made.

To begin with, platinotype printing is divided into cold-bath process and hot-bath process. Of the latter we shall speak later on, but for the present, as being most suitable for the amateur and beginner, we will consider the cold-bath method. The reason for this division and the meaning of the name will be abundantly evident presently.

We first of all procure a tin of paper of the quality marked AA. The paper is put up in tin cylinders containing twenty-four pieces of either 1/4-plate or 1/2-plate sizes, or less for larger sizes. It may, if preferred, be obtained in full-size sheets 20 26 inches.

We have now to bear in mind that the paper is sensitive to daylight to a slightly greater degree than are the silver print-out papers, and hence, whilst handling the paper, placing it in the printing frames, or what not, we need to be a little more careful as to how near the window we bring the paper. At the side of the room furthest from the window, or with an intervening screen between the paper and the window, or yet again, with the blind drawn down, we shall be quite safe in opening our tin of paper and inspecting it.

On removing the lid of the tin we find a false top or cover hermetically sealing it, which has to be cut through in the manner becoming customary with various tinned foods and comestibles.

We then find that the paper within is yellow on one side which is the sensitive side. Within the roll of papers at the bottom of the tin we shall find a hard irregular lump of some substance wrapped round with cotton wool. Keep this in the tin and now note its use from the following:--Platinotype paper is highly susceptible to moisture and deteriorates under its influence. The air we breathe, and therefore the air enclosed within the tin case or any other vessel contains a large amount of moisture, and this moisture would be taken up by the platinotype paper to its own detriment. The presence of water or moisture in the atmosphere or in things we handle, although quite unperceived by us, would be discoverable by the platinum salts on the paper, which would thus become unfit for use, hence the only way of preserving it is by placing in the tin containing the paper some chemical which is even more susceptible to moisture than platinotype paper. Such a body is calcium chloride, and this it is which we find wrapped in cotton wool in each tin tube of paper, or to speak more accurately it is asbestos prepared in a solution of calcium chloride. So long as that little lump remains dry and hard we may be quite sure that it has left no moisture in the air around it for the platinotype paper, and it will go on drinking it up until it becomes softened by saturation, when it must be removed and a fresh piece subst.i.tuted, or it may be restored to its former condition by drying it on a red-hot shovel, the asbestos remaining unconsumed.

Whilst perhaps in after practice we may find it possible to relax our precautions against damp, yet at the outset the necessity of the utmost caution being observed cannot be too strongly insisted upon.

Out of a very large number of prints representing the beginner's first attempts at platinotype, by far the greatest number of failures are due to damp, and this, probably, for want of conception of the danger to which the paper is exposed. Remember then that where there is ordinary air there is also abundant moisture, and as no tin box with a movable lid is air-tight, neither is it moisture-proof, but in the case of our tin of platinotype paper when once opened will go on admitting moisture which the calcium chloride will take up until it can take no more.

After having cut through the inner sealed top of the tin, close up the little hole in the outer lid where the cutting point is with sealing wax, next cover the mouth of the tube with a piece of waxed paper or tinfoil, shut the lid down on to this, and then cover the junction of the lid with a broad indiarubber band. In this way damp may be prevented from gaining access to the inside of the tube to a great extent.

Specially constructed tubes are made which close with an air-tight stopper and have a false bottom with a perforated part.i.tion in which the calcium chloride may be kept. Such a "calcium-tube," as it is called, if not an absolute necessity, is a very desirable acquisition.

If you now take the negative to be printed from and hold it near the fire or a spirit lamp, it will on becoming warm give off perceptible moisture, thus showing that it was distinctly damp before. The negative, therefore, should be dried before being brought into contact with the platinotype paper.

[Ill.u.s.tration: STREONSALCH. W.J. WARREN.]

The wood printing frame itself, if it has been used for printing in the open air, should be placed in an oven or held near the fire to thoroughly dry it.

Having placed the negative and the platinotype paper in the frame in the ordinary manner, there should next be placed at the back of the paper a thin sheet of waterproof cloth, vulcanized rubber of the proper size and thickness being sold for the purpose; this will prevent damp from penetrating to the paper from the back of the frame. The frame may now be closed and placed in the light for printing, and even having taken all these elaborate precautions against damp it would not be advisable to print out of doors except in dry weather, nor should the paper be left in the frame longer than need be, but if it is not proposed to finish the print off at once, it should be returned as soon as convenient to the security of the calcium tube.

GENERAL OUTLINE OF THE PROCESS.

Platinotype paper is ordinarily only available for daylight printing, though the Platinotype Company have introduced a lamp of special construction and great power, by the use of which daylight may be dispensed with, and electric light, should it be available, may be used.

As has been already said, platinotype paper is rather more sensitive to light than silver paper, and hence takes proportionately less time to print.

The duration of the exposure to light const.i.tutes the only real difficulty in platinotype printing, and whilst just at first it may result in the beginner's meeting with much disappointment, yet probably, with a little care and watchfulness the trouble will be surmounted, and sufficient experience gained to secure fairly uniform success thereafter, before even the first tube of paper has been used.

The printed image shows on the yellow ground of the sensitized side as a faint grey, the darkest portions a.s.suming an orange-grey tint, whilst the lighter parts remain all but invisible.

A little practice will enable one to judge the right depth, that is to say, how visible the image should be before printing is to be stopped, but as a rough guide to commence with it may be said that printing is complete when the image is about half as deep as we should expect it to be if it were a "print-out" process.

As we shall have occasion to return to the question of printing presently, we may now pa.s.s to the next step in the process.

In twenty-five ounces of hot water dissolve half a pound of best neutral oxalate of potash, and keep this in a stoppered bottle as stock solution. What is known as _neutral_ oxalate should be used, and in order to ensure having a suitable salt it had better be obtained from a recognised photographic chemist or dealer.

As the above solution becomes cool, a good deal of the oxalate will probably settle at the bottom in the form of solid crystals; of these no notice need be taken, for as long as there are undissolved crystals at the bottom of the bottle we know we have a saturated solution.

We shall now require a dish of porcelain or enamelled iron, and if we choose the latter great care must be taken to see that the enamel is not cracked or blistered, as it will have an injurious effect if the oxalate of potash solution obtain access to the iron under the enamel.

As it will be convenient to be able to alter the temperature of the solution when in this dish at will, a spirit lamp or stove or a small gas-stove will be a useful, if not an essential addition. Over such heating apparatus the dish should be supported on an iron tripod, or by any extemporized subst.i.tute.

If a porcelain dish be used, a thin sheet of iron should be placed first on the tripod stand, and then three or four sc.r.a.ps of iron, large common iron nails will serve very well, and on these the porcelain dish is allowed to rest so that it does not come into direct contact with the iron plate.

The purpose of this is to save the dish from cracking, moreover the iron plate becomes hot, and retaining a good deal of heat serves as a kind of acc.u.mulator which goes far to maintain the dish and the contained solution at a uniform temperature for at least a short time. Even better than this arrangement will be an iron dish filled with clean dry sand, the porcelain dish to rest on the sand which retains much heat.