Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: incompletefool on 18/11/2012 21:54:43

Title: Moisture sensitive color
Post by: incompletefool on 18/11/2012 21:54:43

A little help, please.
   
   I am looking for an ecologically safe alternative to cobalt chloride.
   In other words I am looking for a humidity/moisture sensitive chemical/color/pigment that is earth/life friendly, relatively inexpensive, self reversing, long lasting,....and probably doesn't exist.
   When I try googling the question I either get products I don't need that reference using something like that, but they don't tell me what it is, OR, I get chemical formulas which are greek to me.
   I would like to get a small quantity of such a chemical so I can test an application and hopefully demonstrate proof of concept.
   Any help would be greatly appreciated.
Thank you.

Title: Re: Moisture sensitive color
Post by: damocles on 22/11/2012 22:37:11

It is hard to say whether anything not naturally present in the local environment is "ecologically safe". Copper(II) compounds are quite toxic, but less so than cobalt compounds. Copper(II) sulfate is readily available and relatively cheap in the form of sky-blue crystals. When these are gently warmed the water of crystallization (copper(II) sulfate is a pentahydrate) is lost, and a colourless powder of anhydrous copper(II) sulfate is formed. This material is hygroscopic (i.e. it will absorb moisture from the atmosphere), returning to the blue colour of the original crystals. It is not as fast responding as cobalt(II) nitrate, and the blue colour is less intense, but it might serve the purpose that you are looking for.
Copper(II) compounds are widely used in agriculture, horticulture, home maintenance, etc. as algicide or fungicide

http://chemicals.etacude.com/c/copper_sulfate1.php (http://chemicals.etacude.com/c/copper_sulfate1.php)

Title: Re: Moisture sensitive color
Post by: CliffordK on 23/11/2012 16:56:34

Perhaps rather than going from blue to pink, you could simply get a moderate color shift.  Many substances will produce a moderate color shift when saturated with water. 

Would the color shift be more pronounced in different parts of the spectrum?  A computer analysis might be able to detect and quantify the color changes from saturation of your target substance.