Homebrew PCBs

Can you confirm / deny this formula from "files" here is appropriate? 

"I have successfully used 2 parts 3% medical H2O2 with one part 31%
acid - no additional water. It's pretty close to the same mix when
you're done. Etching times of 7-10 minutes."

I used this same formula at room temperature and etch was faster than
7-10 minutes with a bubbler. But no bubbling on its own. 

BTW, I found out the hard way, the oxygen "bubbler" you put in the
etch tank needs to be plastic with this etch solution - I used
aquarium bubbler "stones" and they disintegrated. Makes sense in
retrospect, hardware stores sell muriatic acid to clean brick and stone.  

Bob


--- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan"
<stefan_trethan@...> wrote:
>
> Yes, check the links section.
> The two-eyedropper method is best to check molarity sometimes while
you  
> start the solution.
> 
> You don't need to put in any copper or copper oxyde or something,
it's OK  
> to start with a slightly strong acid and add H2O2 each time in small  
> quantities. The CuCl will build up all by itself from the boards.
> 
> When way too strong it is mostly oxygen gas, yes, but it also can
get hot.  
> HCl boils very low, and you can quickly get loads of HCl fumes.
There have  
> been some accidents with this etchant industrially, where it
elegedly did  
> "go through walls" and even killed people when way too strong. This
is not  
> so dangerous in household quantities, but you should not have a
violent  
> bubbling and you should always have it inside a second larger
container  
> that also takes some diluting water in an emergency.
> Note that when it is so strong it will also underetch and eat all
markers  
> easily. I know what i'm talking about, when i started with it i once
timed  
> this etchant at 11 seconds a board (luckily in tiny size/quantity).
> 
> ST