On 17/02/14 13:19, Philip Pemberton wrote:
> On 17/02/14 01:15, Russell Shaw wrote:
>> Foaming is usually a sign the liquid viscosity is too high. Long etching times
>> are a symptom of that too.
>
> That's interesting - I've never seen viscosity mentioned as a control
> parameter for cupric chloride etchant.
>
>> The active ingredient should be diluted 1:1 with water. Add a few percent (like
>> half a cup) of hydrochloric acid too. When topping up is need every few months,
>> just add more hardware shop hydrochloric acid (it has water in it anyway).
>
> Are you suggesting I dilute the etchant I have one-to-one with water?
> That sounds like it'd send the specific gravity crashing through the floor.
If you started with concentrated ferric chloride, it should be diluted 1:1 with
water. The water gives "room" for the reactants. I'm assuming the ferric
chloride was bought in liquid form. If it was obtained as dry powder, i'd add
just enough water to dissolve it, then add another equal amount of water again
(as a first guess, but maybe more water would be better). Add some HCl acid too.
You could tell how diluted the existing mix already is by comparing the weight
of your etchant to the weight of concentrated ferric chloride.
> I'd sooner add peroxide to it, at least that'll oxygenate it while it's
> reducing the SG...
That would be ok for the first go. After that, the normal bubble agitation will
keep the oxygenation good.
>> With a setup similar to yours (but working properly), full etch happens in
>> 12mins at room temperature.
>
> I'd consider that more than acceptable seeing as my ferric chloride tank
> takes a little over twenty minutes :)