# ...acid?



## markgriffith (Jun 9, 2008)

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Hello everyone. I'm looking for something photosensitive which is mildly acidic, but then can be safely fixed. 

I want to experiment with some crude etching ideas - coat various soft substances with something that turns acidic once exposed to light and then, under the image, watch the light-exposed areas of coating eat into the surface. 

So 2 problems really. 1 How to get a substance that is photosensitive and turns into a mild acid on exposure to light, and 2 How to stop the corrosive action with a fixer. 

Any ideas most welcome! Thanks...

Mark    http://www.otherlanguages.org

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## markgriffith (Jun 9, 2008)

Don't all rush at once...!


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## compur (Jun 9, 2008)

The closest thing I know of to what you're asking is photo-etching.  But,
acids are added during the process rather than being formed by exposure to
light in the way you describe.  Search for photo-etching for more info.


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## Alpha (Jun 9, 2008)

The only thing I can think of would be some sort of alkane with both halogen and acidic functional group (acetyl perhaps). You'd run into problems, though. I'd have to go back and consult my organic textbooks. It would have to be something that was stable in anion form so that it could form a silver salt. Anion stability makes me think small, or conjugated, though I have no idea what a small molecule like that would look like, and a conjugated molecule probably wouldn't be reactive enough.

Try asking on APUG. There are some real chem-wizards there.


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## Rhys (Jun 10, 2008)

I know the stuff you want - they use it in electronics circuit board etching. The fluid's available from most electronics stores.


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## Helen B (Jun 11, 2008)

I can't think of anything that does exactly what you want. The photo-resists used in electronics circuit boards have already been mentioned by compur, and he has pointed out the difference between what you want and what they do.

It's easy to find something that hardens  as light strikes it (ie where the light strikes, the substance remains), but that would not give you exactly what you wanted - close, but not quite. You could start a slow removal process, then watch as the light-struck parts prevent further erosion. 

One of the main things is that whatever process it is, it mustn't be too sensitive to the wavelength you are using for observation. This isn't a big problem, but it does mean that you may have to have some control over the viewing conditions.

Google for gum printing and photopolymers - one old technique and one new. Browse through a few 'alternative' processes: here is a good place to start. 

Good luck,
Helen


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