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I have some old circuit board etching solution (ferric chloride) that is unused but a few years old and has not been in a temperature controlled environment. It has been sitting, all but forgotten, on a shelf in my garage.

I'd like to etch some small boards this weekend, but would rather not ruin them with old chemicals.

Should I just go ahead and use it or buy some new etchant?

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I have successfully used ferric chloride from a ten year old bottle. It was stored in my house though, not the garage.

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I have a really old bottle of FeCL as well, and wondered if it's still good.

I was able to find this post by Mike Blue on a forum:

Iron containing alloys consume the available HCI in ferric chloride solution. The HCl is the major active etching ingredient. The generally accepted shelf life of ferric chloride solution is approximately six months. Adding HCl acid can restore the cutting ability of the FeCl3.

(Emphasis mine.)

Since I don't want to mess with obtaining or working with hydrochloric acid, I think I'll just get a new bottle next time I need to etch a board (which may never happen, given how easy it is to get prototype boards from the likes of OSH Park and others).

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    \$\begingroup\$ Ferric chloride solution will last indefinitely if it is unused. There is no chemical reason for it to deteriorate. \$\endgroup\$ – Leon Heller Oct 13 '14 at 19:58
  • \$\begingroup\$ @LeonHeller: I thought that might be the case, but my chemistry knowledge is "rusty" (sorry for the pun.) \$\endgroup\$ – Edward Oct 13 '14 at 20:39
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Calibrate the time of exposure to the solution, it may not be the same as new but the solution sits on shelf before you buy it. May change from some sort of reaction to bottle and atmosphere and light exposure driven reactions. I have used solutions that were hyper old but the other guy says 6 months. If I thru away everything 6 months old I would have clean house and no materials to dink with.

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