The course of the photochemical etching process

photochemical etchingA uniform application of the emulsion can be achieved, pouring it from a low height onto a horizontally placed metal plate. Perfectly helps to make the plate rotate; rotational speed should not be greater than 160 rpm. A suitable drawing with the dimensions of a metal plate should be made on tracing paper or transparent foil. Places, to be etched,should be carefully blackened, places, convex - leave transparent. Use such a plate to irradiate the plate covered with the emulsion from such a distance, so that the entire surface of the plate is evenly illuminated. The exposure time should be selected by the trial method, as it depends both on the type of emulsion, as well as from the light source. Indicatively, you can take, that lamp irradiation, giving light similar to daylight, lasts 10…15 min, halogen bulb – 5…7 min, and a quartz lamp – 2…3 min.

After irradiation, the uncured emulsion is removed for 15…20-1 minute bathing in water with the plate constantly moving. The shellac emulsion is dissolved in 0,1 -a percentage solution of methyl violet in ethyl alcohol (simply denatured alcohol can be used, which is usually dyed with just methyl violet).

If a dilute acid solution is used for pickling or, as with copper etching, ferric chloride solutions – it is not necessary to additionally protect the non-rinsed emulsion layer. However, better results are achieved by coating the protuberances with asphalt varnish with a rubber roller. Etching is carried out after the varnish has dried. The shellac emulsion can be fixed in a bath of 20 g kalafonii, 10 cm3 of ammonia water, 4 g of methyl violet i 300 cm3 denatured. Po 3 min to remove from the bath, rinse with water and dry through 30 min at room temperature and 30 min w temp. 80°C.

After the plate is etched and rinsed, the remaining emulsion is removed by soaking it in a few percent sodium hydroxide solution. If the metal is aluminum or its alloy, remove the emulsion, by soaking it for several hours in 10% sodium carbonate solution or in boiling water.

Non-etched areas can be stained permanently, by applying any varnish with a rubber roller. The etched depressions can also be tinted, not caring too much about the sharpness of the contours, and rub off excess varnish with sandpaper, lying on a flat, a hard pad, e.g.. glass plate.

The described method has received a lot of attention, because it can be used in many variants. After inking the gelatin or etched protrusions with ink, the plate can be used as a printing plate. You can also etch drawings on plastics, using suitable solvents for etching. This method also allows you to perform the so-called. photos fired, often found on tombstones. Painting patterns on fabrics using the method is also based on similar principles printing sitowego.