THE PHOTOGRAPHIC NEWS. VOL. II., No. 44.--July 8, 1859, p.205

TONING WITH PLATINUM

SEVERAL years ago I had an opportunity of proving the truth of the old adage--" Necessity is the mother of invention." I accidentally found myself without any chloride of gold, and having no nitric and hydrochloric acid by me at the time, with which I could have dissolved a piece of gold, and thus overcome my difficulty, I was in what is usually called a "fix "--that species of "fixing process" which photographers care least about. It occurred to me, therefore, to try whether the chloride of platinum would answer the purpose of toning as well as the chloride of gold.

Having by me a strong ethereal solution of the chloride of platinum, I made up a toning bath thus:--

I dissolved four ounces of hyposulphite of soda in eight ounces of water: I then added about 60 drops of the chloride of platinum to an ounce of distilled water, which I then poured into the hypo. solution, gradually stirring all the time, in the same way that the gold is treated when making ; gold toning bath. The platinum readily entered into combination with the hypo., forming a clear solution.

I now took an over-printed proof, and immersed it in the bath, and to my great astonishment and delight, the proof, in the course of a minute or two, assumed a beautiful dark brown colour, superior in tone to any shade of brown I have ever known to be produced in a gold toning bath. It appeared me that in two minutes the proof had acquired the maximum of coloration, for on allowing it to remain for a much longer period no apparent- alteration took place. In some instances, where the proof had not been much over printed, the toning seemed almost instantaneous.

Having used Sutton's toning baths a good deal at that tine, it occurred to me to make a bath, after his formula, substituting platinum for gold ; and, after having well washed some proofs, as directed by him, in the process referred to I plunged them into the newly-made platinum bath which consisted of--

I dissolved the hypo. in 3 ounces of the water, and dropped chloride of platinum into one ounce of the water (this should be distilled water). I then carefully added the platinum solution to the hypo., well stirring. Lastly, I added the hydrochloric acid.

Instantly the proofs assumed a rich and brilliant brown colour, of a beautiful tone. I then fixed the proofs in a strong solution of hypo. and the whites became at once perfectly clear, whilst the general tone of the proofs did not, as I can remember, undergo any evident alteration.

After having made repeated experiments with the platinum toning bath referred to, in various ways, I felt quite satisfied that with this bath it is possible to obtain brown tones far more beautiful than any shades of brown which can be obtained in a gold bath.

I did not find that by leaving the proofs for any longer period in the platinum bath, the tone would alter from brown to the shades of purple or black, as in the gold bath, and I am inclined to think that such would not be the case.

I have been desirous of conducting these experiments again, with a view to lay before the photographic world some quantitative data, which would prove -whether or not the platinum bath is more economical in use than that prepared with gold. My impression is that with care, and by using a bath soon after it is made until it is fairly worked out, it will prove to be an inexpensive one to work, especially if photographers make their own chloride of platinum.

Amongst the many experiments which I made with platinum was the following :--

In the place of hypo. I employed a few grains of cyanide of potassium in the new toning bath, and I have a proof by me which I took from the pressure-frame, toned and washed it in several waters (one water being warm), ten minutes altogether, and thus proof has been exposed more or less to the influences of the atmosphere and light ever since, without apparently having undergone any change. This was done fully three years ago.

After observing, practically, the effects which the platinum produced upon the reduced chloride of silver on the proofs, I began to reflect a little upon the theory of the subject, and the following deductions occurred to me at the time.

I had for some years observed that when an ethereal solution of chloride of platinum was placed in contact with a surface of silver, it immediately darkened the surface, and, as the ether evaporated, a film of reduced platinum was deposited upon the silver, which would attach itself so firmly that it would require good hard rubbing-- although the layer was necessarily exceedingly thin-- to remove it. This, I argued, would favour the permanency of proofs toned with platinum, for in these we have a silver surface, which, in the process of toning, the platinum attaches itself. Now, as platinum is, of all metals, the least likely to be affected by atmospheric influence, or by light, or even by any hypo. which may be left in the paper from under-washing the proof, I think that- proofs toned by it will be more likely to be permanent titan others toned in any way. Of course this is merely an opinion. I acknowledge that I have not yet sufficiently tested the peculiarities of time process, owing to the fact that my time has generally been most fully occupied whets I had time greatest desire to renew my researches.

If any of your numerous readers should feel disposed to try the platinum toning bath, I should recommend them to proceed thus :--Owing to the quickness with which time baths tones, it would be advisable, I think, either to wash the proofs first, or to fix them in a plaits hypo. bath, 4 ounces to 8 ounces of water, and then to wash them a little before placing them its the toning bath, when I have no doubt the tone will be acquired almost immediately after immersion. But this, I believe, will depend upon the amount of platinum in the bath; therefore, when time is an object, I would recommend employing plenty of the chloride, which, although it will augment the speed of the operation, will not involve much greater cost, for I do not conceive that the reduced silver upon the surface of the proof is capable of attracting, if I may use the term, more than a certain quantity of the metal from the toning bath, whether it remains in time bath up to the time that the picture is toned, or for a week afterwards.

About two years ago, I called Mr. George Knights attention to this new toning bath, but I have not yet had an opportunity of bearing what success he met with.

Should any of your readers turn their attention to tins subject, I shall be most anxious to hear the results of their labours, and I do hope that they may derive some advantage from the process, which, with a little care, I have no doubt will do.

In conclusion, I may remark that I had intended long since to have made known the above process, but other matters have prevented me from doing so.