Photoetching at home
Photoetching at home for the model maker
by Andy Slater
Perhaps the key feature of any photographic process is that things can be enlarged or reduced in size and this is certainly the key factor with photo etching as it relates to model making.
Etching (as pertaining to photo etching) is a chemical process where metal is eaten away by acids. The trick is to apply a protective coating to the parts of the metal that you want to keep. In the world of modelling it is most commonly used to etch thin brass sheet to produce cockpit details for aircraft, windows and doors for buildings and even miniature plants like ferns. Bear in mind that although the brass sheet starts out flat there is nothing to stop you from bending it into some other shape after it has been etched.
Additionally, if I may be pardoned for going off on a slight tangent, all be it a relevant one, the photographic negative required as a part the process has uses in its own right. A splendid example of this is in the production of instrument panels. In this instance, you could etch holes into a sheet of brass and then mount an actual photographic negative, with the instrument detailing upon in, behind the brass.
The Photoetching Process
Create the artwork
There are a few things that need to be borne in mind (see below) when creating the artwork but the main thing here is, as already mentioned, that the artwork can be larger than finished result. This allows for a greater level of detail to be drawn than would be feasible if the artwork had to be produced actual size. You should also endeavour to achieve a high contrast i.e. black on white, with the artwork as this will help with the next step.
Create a negative on photographic film
Although it is possible to photograph the artwork yourself there are a number of reasons why finding a local lithographer (check the phone book) to do it for you is a better bet. The first is that a high contrast litho-negative will produce a much better finished result. The second is that the lithographers' camera is geared up for doing accurate reductions. If you say you want a 25% reduction, that's what you'll get. Doing it yourself is going to require that you do some calculating and even then it is likely to be a bit hit and miss. The final reason is that by the time you've run a whole film through your camera and got it developed, it'll probably work out more cost effective to go to a lithographer anyway.
Transfer the design to the brass
First of all we need to make the brass photosensitive so after giving it a rub over with fine sand paper to remove oxidisation and a rub over with alcohol to get rid of any grease, it should be given a couple of coats of photo resist. Photo resist (and all the other chemicals used here) are readily available from electronic supply stores as they are also used in the production of printed circuit boards. Bear in mind that the whole point of this chemical is that it is light sensitive so this part of the photo-etching process should be performed in subdued lighting. The chemicals are designed specifically to react with ultra-violet so sunlight should definitely be avoided while low level domestic lighting will be fine.
Leave the photo resist in a dark place to dry
In order to get the design onto the plate you now have to fix the photographic negative to the brass and expose it to ultra-violet light. It is essential that the negative is held flat against the brass so the best method is probably to place the brass onto a hard surface with the negative on top and a piece of glass on top of that to hold it flat. It can be exposed by leaving it on a window sill where sunlight can get at it but a faster and more reliable result can be obtained using a UV-light source (also available from electronic supply stores).
Unfortunatly, this part of the process has no visible effect on the brass and getting the correct exposure is a case of exposing it for the length of time stated on the photo resist.
Developing and Etching the Plate
Before we can start etching we have to develop the plate. This is a chemical process which removes those areas of the photo resist that were not exposed to UV while turning the areas that were into a protective coating that will stop those areas from being etched. Once again, you should work in subdued lighting because the coating on the brass will be light sensitive until after it has been developed. (After developing you can go back to working in normal lighting)
Dilute the developer with water in the ratio given on the instructions and place the plate in it for the required length of time. You will be required to agitate the solution during the development process but this does not need to be at all vigorous. My preferred method is to use a shallow plastic container like the bottom of a yoghurt pot. I find that this will accommodate most photo etching projects and requires only a only small amount of chemicals be used. Agitation is done by tipping the pot to one side to create a wave in the liquid every 30 seconds or so.
When the plate is developed it can be rinsed in water. It is now safe to expose it to bright light and after it has dried you should give it a close inspection. Some photo resist chemicals change colour when they are developed while others just leave a shiny transparent layer that can be viewed by holding it up to the light. Either way, you should inspect the plate because if you spot any problems with the coating at this stage you can simply clean it off and start over again.
Providing that the plate looks good, you can move on to etching it. This is another process similar to the developing except that you can now work in good light. In fact you'll need to because this time you'll need to inspect the plate at regular intervals to see how it's going. The plate should be left in the solution until all of the brass that is supposed to be etched away has been. Probably something like fifteen minutes.
Now all you need to do is rinse it in water and using fine sandpaper, clean off the coating of photo resist.
Things to Bear In Mind
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