Talk:Photochromism
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[edit] Photochromic dye
Here's some content than was in a different article. I think that it is best covered here, so photochromic dyes now redirects here.
The word photochromic is defined as a compound that has the ability to change colour when exposed to light. In the presence of light a photochromic compound will turn dark in colour and the effect can be reversed when light is absent. Photochromic compounds are sensitive to changes in light of differing wavelengths. This property of photochromic compounds has been used by scientists to create a new smart material. These smart materials are photochromic dyes. As the name suggests photochromic dyes are substances used for colouring/staining surfaces (like normal dyes) but which possess a photochromic characteristic. Thus, when the dye is applied to a desired surface the colour on the surface will change colour accordingly. Dyes are soluble substances which have a less stable pigmentation than paints. Dyes are generally not used for cards but are rather designed for fabrics and hair. Therefore, photochromic dyes give rise to clothes that are sensitive to light exposure or hair that has the ability to change colour.
-- Kjkolb 09:38, 3 February 2006 (UTC)
[edit] Irreversible Photochromics - Do they really not exist?
This section in the article basically says the name of the effect, and then says it never happens. I don't think this is true, but I am not enough of an expert to say for sure.
What about chemicals used in photographic processes? For example, a contact print is done with a chemical that has a permanent change in color when exposed to light. Similarly, when you make a circuit board (with photoresist) or a screen for screen printing (using photoemulsion), the reacted stuff has a change in color before you wash away the unreacted stuff. That most definitely is irreversible, but it's not a huge color change. Hopefully someone smarter than I can show up and explain this
--Shrodingerskitty 20:44, 28 March 2007 (UTC)
- I think you might want to read that section again. Of course there are irreversible color changes, but the term "Photochromism" is, by definition, only for reversible processes. Thus, any irreversible processes are not photochromism. Just the definition. okedem 23:31, 28 March 2007 (UTC)
