> Like others have said. Don't have too much acid. High acid will increase
> etch speed, but the consequences are fuming and corrosion as you are
> experiencing. Of course if there are splashes and micro droplets finding
> there way to surrounding items then unwanted corrosion is inevitable. If
> you ever had a fish tank with aerator and no cover, you may of found
> water splashing a foot radius or more. The etching tank ∗must∗ be
> covered with a lid when bubbling. I have noting more than 3mm slit
> opening in the lid , just enough for the PCB, and even so there are
> splashes.
>
I lay down several layers of newspaper under my etching tank to catch the mist. If the tank is particularly full or foul weather forces me inside, I lay a paper towel across the top of the tank to keep most of the mist from getting out.
When finished, I pour the etchant into a clearly labeled sealed plastic bottle for storage and rinse out the tank with baking soda water. Unless you etch a lot of boards on a regular basis, I highly recommend storing the etchant in something that can be tightly sealed. If the tank gets knocked over somehow you'll have a real mess on your hands.