Unusual photo. Fun chemistry experience at home

ENTERTAINING EXPERIENCES AT HOME
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Unusual photo. Chemical experiments

Entertaining experiments in chemistry

Entertaining experiences at home / Chemistry experiments for children

The photographic process is based on the transformation of light-sensitive substances - silver halides, most often bromide. Being in a light-sensitive emulsion, they disintegrate under the action of light, and tiny crystalline nuclei of silver appear on the illuminated areas.

And silver is a precious metal, needed not only for photography. And so researchers are looking for such light-sensitive substances and systems that would not contain silver. There are also successful finds along this path, but a full-fledged substitute has not yet been found. However, for some purposes, a photograph without silver or almost without silver is successfully used. And such unusual processes can be reproduced independently. Here are some examples.

Dissolve 100 g of glucose and 15 g of ammonium bichromate in 2 ml of distilled water. Soak a clean thin white cloth with the prepared solution and dry it, but always in the dark, because it has become photosensitive, and iron it in the dark. Prepare the developing solution in advance. It consists of 1 g of silver nitrate (it is impossible to do without silver salts at all) and 10 ml of acetic acid per 100 ml of water.

Draw on the tracing paper the image that you would like to transfer to the fabric. Lay the tracing paper on top of the fabric and expose to daylight. Take your time; for the photochemical process to be completed, it will take about five minutes, and even more with electric lighting. To develop, dip the fabric into the developing solution. Complete darkness is no longer necessary, weak ambient lighting is acceptable.

Dry the developed fabric; It has a dark brown design on it.

In this experiment, you took advantage of the reducing properties of glucose - it reduced chromium in ammonium dichromate. And the bichromate that did not recover reacted with silver ions from the developer, forming a colored compound, which remained on the fabric, since it is insoluble. And because the coloration appeared in the unlit areas, you got an immediately positive image.

Another version of this method, also with ammonium dichromate, but without glucose and, more importantly, without silver, even in the developer. Prepare an emulsion consisting of two solutions. First solution: 17 g of wood glue and 6 g of gelatin, pour 100 ml of water, add 3 ml of an aqueous ammonia solution and leave to swell for a day, and then heat for about an hour in a water bath at 80 0C until completely dissolved. Second solution: 2,5 g each of ammonium bichromate and chromium potassium alum, 3 ml of an aqueous solution of ammonia, 30 ml of water and 6 ml of alcohol. When the first solution has cooled to about 50 ° C, pour the second solution into it with vigorous stirring and filter the resulting emulsion twice (preferably through cotton wool). Put it in a dark place, and the next operation - applying the emulsion to a metal, glass or ceramic plate - is carried out in a darkened room.

Pour the emulsion heated to 30-40 ° C in a thin stream onto a clean plate, shaking it to even out the layer. Dry the plate for ten to fifteen minutes, preferably with a slight heat, and, as in the previous experiment, put a tracing paper with an image on the photosensitive layer. Press it with glass to straighten it, and light it up. A few minutes in the bright sun is what you need, and if the lighting is artificial, then turn on for 10 minutes several lamps with a total power of about 2000 W, preferably with reflectors.

It is necessary to develop immediately, otherwise chromium salts will kill gelatin where it is not necessary. Developer - a little warm, not more than 30 ° C, water. Uncured gelatin will dissolve in it. And those areas in which gelatin proteins have hardened under the action of light will remain on the surface.

The image is not very clear. To correct this deficiency, dip the print in a 1% solution of methyl violet indicator (you can use diluted violet ink). Rinse the plate in water and proceed to fixing in a solution: 5 g of ammonium dichromate, 2 g of potassium chromium alum and 4 ml of alcohol per 100 ml of water; time is three or four minutes. Air dry the photo. To further secure the image, you can heat it for several minutes in a drying cabinet or in the oven.

We will make the next silver-free photo more familiar - on paper. True, on the filter; but still - this experience is a demonstration.

Dip a circle of paper into a solution containing 20 ml of 5% solutions of red blood salt K₃[Fe(CN)₆], iron chloride FeCl₃ and oxalic acid H₂CO₄ (carefully!). Remove the impregnated paper from the solution and dry in the dark, then lay the tracing paper with a pattern and shine it in sunlight. Incandescent lamps are not suitable for this purpose, but an ultraviolet (quartz) lamp is suitable. Lighted areas will turn dark blue due to the formation of the already familiar turnbull blue. No development is needed, and to fix, rinse the paper with water to wash off substances that have not reacted.

And the last experience with a silver-free photo. In one glass, dissolve in 100 ml of water 0,4 g of iron (III) chloride and oxalic acid, in the other, 1,4 g of copper chloride in the same amount of water. Mix 10 ml of the first and 0,6 ml of the second solution, saturate the filter paper with the mixture and dry it in the dark. Prepare the developer: 3,5 g of copper sulfate, 17 g of Rochelle's salt (double sodium-potassium salt of tartaric acid), 5 g of caustic soda (carefully!) in 100 ml of water and mix with 25 ml of a 40% formaldehyde solution. Shine the paper again in sunlight or under an ultraviolet lamp through a patterned tracing paper; unlike the previous experience, the image is not visible at first. It will appear after 15 minutes exposure in the developer and washing in a large amount of water.

This process is somewhat reminiscent of a silver photograph, since crystallization centers are also formed in the photosensitive layer, but not silver, but copper; however, copper was deposited not from an emulsion, as in conventional photography, but from a developing solution.

Author: Olgin O.M.

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