About etching again

[rockhorst]

This weekend I tried to etch a box with what I think is a pretty nifty design  Followed the instructions from the etching album as far as methodology goes. I had ordered some etchant powder for PCBs (ammonium persulfate). That was the only thing I had at hand so I decided to give it a try. I dissolved it into the prescribed 0.4L of water. Long story short: the box stayed in the etchant (heated au-bain-marie to about 40^oC) for well over 5 minutes, with some wisking and checking and showed not even a TRACE of acidic wear n tear.

My best guess is that the used etchant is designed for thin layers of copper used in PCBs and isn't strong enough for big bulky aluminum boxes...Does that make sense?

[darron]

when i use that stuff to etch pcb, even floating in warm water, it can sometimes take HOURS!

the temperature sounds good, and if you had exposed aluminium then there's nothing wrong there. suggests you MUST use a different etchent. buy liquid ferric chloride. don't buy powdered ferric chloride.

if suppose the good news is that you didn't waste an enclosure if it didn't etch a trace? give it a sand and try again

[brett]

Hi
the main tricks with ammonium persulphate are: 1. use about 1 part AP to 5 parts water (10 max), and 2. keep it hot - about 70C/150F, which coincidentally is about the temperature of water coming out of the hot water tap (/fawcet) or the kettle two minutes after it boils.

Agreed that ferric chloride works better with aluminium.  Hydrochloric acid is cheap and has a similar action to ferric chloride (ferric chloride produces hydrochloric acid and ferric hydroxide), but can be more hazardous if concentrated.  Something around 10% HCl might be worth a try.
cheers

[rockhorst]

At the hardware store they sell <10% HCl  wich is apparently used diluted to clean windows and such...Weird, but if I can't find etchants at the artstore or something similar I'll give that a try...

@Brett:
-you mention 5 part water on 1 part AP...I take it that's weightpercentages?
-In what way is HCl more hazardous dan FeCl? Do you mean fumes and such?

[John Lyons]

2 parts Hydrogen peroxide (3% as you get at the drug store etc.) to one part Muratic acid/ Hydrochloric acid (28%) works fine for etching copper boards, take about 5 minutes or less, I would think it would do fine for Aluminum as well. You can get the Hydrochloric acid at most hardware stores. No need to heat it up.

John

[lovekraft0]

For etching aluminum, here's a method developed for printmaking that uses industrial-grade copper sulfate (a fairly common algicide), sodium chloride (table salt), and sodium bisulfate (Sani-Flush®):

Using a Safer Mordant Intaglio Etching on Aluminum and Zinc

It's worth a look, particularly if ferric chloride etchant is eating up your fine detail work or causing other problems. Keep in mind that just like ferric chloride and hydrochloric/muriatic acid, all these chemicals are potentially toxic and/or corrosive if handled improperly - don't hurt yourselves.

[sta63bmx]

What kind of finish is there on the aluminum?  If it's clear anodized at all, the etchant may have no effect.  I ran into that trying to etch a piece a while back.

[rockhorst]

It's a sanded down Hammond box.