The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Bromide Paper
Conversion of the Image into Platinum. The silver image of the bromide print may be converted into platinum by the following process, first suggested by Vidal in 1887. The well-washed print is immersed in the following bath: -
Platinum perchloride         ......... 1 part.
Distilled water ...... ... ... 2000 parts.
Hydrochloric acid ... ... ... ... 25 ,,
till the desired tone is obtained. E. Vogel, junior, recommends the following -
Chloroplatinite of potash ... ... ... 1 part.
Distilled water         ... ... ... ... 1000 parts.
Hydrochloric acid ... ... ... ... 10 ,,
The print is placed in this for about twenty minutes, and is then thoroughly washed and fixed. To prove the substitution of platinum for silver, place the print in a solution containing cupric chloride made as follows : -
No. 1.
Calcium chloride, crystal....., ... 10 parts.
Distilled water         ... ...... ... 50 ,,
No. 2.
Sulphate of copper, crystal           ... ... 15 parts.
Distilled water ... ... ... ... 100 ,,
When the salts are dissolved, mix the two solutions and pour on to a filter paper, and allow the filtrate to drain through, and wash the filter paper with 50 parts of distilled water. The print, or a portion of it, is soaked in the filtrate, when any silver remaining in the image will be converted into chloride,' and may, after washing, be removed by the use of the ordinary fixing bath ; or if the image appear pale and wanting in intensity, it may be redeposited in the shape of metallic silver by applying an old ferrous oxalate developer. If the print, after being treated with the cupric chloride solution, be exposed to actinic light, the image can be developed in shades varying in colour according to the duration of the second exposure.
Failures.
The exposure has been over-estimated; in other words, the
enlargement is over-exposed. This is at once recognised by the
resulting print being flat, wanting in contrast, or sunken in. The
whites even may not be pure, but show signs of reduced silver ;
100