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David Fairfield
09-08-2008, 1:29 PM
Anybody know if this stuff will work on brass as an acid resist for metal etching ?

Dave

Rodne Gold
09-08-2008, 2:02 PM
No , I tried it , comes off and is somewhat "pourous" in that large areas dont resist properly. Woulda been nice tho , but then again , if it stuck and worked , one woulda had to struggle to get it off.
A sharpie or paint works , you can draw with a sharpie and it wont etch there - easy to remove with thinners after. You can also spray paint with an etchcoat and then a automotive laquer atop that , laser thru it all. Use a bit of handy andy on your fingertips to clear off any residue where it's lasered and then etch. Problem is , if you leave it a long time in the etchant , the resist comes off and gets undercuts in fine detailed work , like you lose the middles of "a's.
By far the best resist is the polyester shiny vinyls , you can both kiss cut large areas and then vaporise small ones , tho you need to sandblast after to clear the glue residue.
As an aside , we never cerdec anything where the metal tarnishes (brass/silver/gold) as commercial jewellery cleaners often contain Phosphoric acid which seems to attack the cerdeced (note im using that term as a generic for whatever metal marking you do) sections , and cleaning with abraisives like brasso , eventually wear it off too.

Mark Winlund
09-08-2008, 2:28 PM
If you want to reduce the undercut to almost nothing, put an aquarium airstone in the bottom of your etch tank, and the workpiece just above it so that the bubbles hit it perpendicular to the surface. Ventilate, and don't lean over it and breathe the fumes.

Mark

Rodne Gold
09-08-2008, 2:40 PM
I have found that its the time in the etchant that counts re undercutting , so we try shorten etch times
What we do is have a sump of ferric heated with 3 x 300w Aquarium heaters and this is sprayed thru irrigation spray mist nozzles hitting the plate from the underside (plate is face down), the Ferric is heated to 45 degrees c and is laced with citric acid ( http://www.polymetaal.nl/beguin/mape/edinburgh_etch.htm ) and this is real fast , up to .1mm per minute in brass and ally. Even quite fragile resists can survive the short etch times despite the higher temps.

Jack Harper
09-08-2008, 2:52 PM
If you want to reduce the undercut to almost nothing, put an aquarium airstone in the bottom of your etch tank, and the workpiece just above it so that the bubbles hit it perpendicular to the surface. Ventilate, and don't lean over it and breathe the fumes.

Mark

Mark - Can you explain this a bit more? Do the air bubbles serve as an agitator for the acid against the surface? If so, what would stop the air from just getting trapped in the etched area preventing further acid contact? Also, would you want the entire surface being etched to have a matching aeration stone below it, i.e. a 24"x24" etching to have a 24"x24" aeration stone beneath? Thanks for the follow up.

Brian Robison
09-08-2008, 3:10 PM
I've done a little research on the acid etching but I still haven't found where to get the different kinds of acids and what one to use for what.

Mark Winlund
09-08-2008, 8:11 PM
Mark - Can you explain this a bit more? Do the air bubbles serve as an agitator for the acid against the surface? If so, what would stop the air from just getting trapped in the etched area preventing further acid contact? Also, would you want the entire surface being etched to have a matching aeration stone below it, i.e. a 24"x24" etching to have a 24"x24" aeration stone beneath? Thanks for the follow up.

The rising bubbles provide a pumping action against the face of the workpiece. The whole container full of etchant will start circulating. Of course, I am talking about flat items... nameplates, pcb's, etc. There is a lot of circulation going on. The function of the bubbles is to bring fresh etchant to bear. Contrary to common belief, the worst way to etch (when considering undercut) is to place the workpiece in a tray of still etchant. Only one or two stones are required for doing a single item at a time. The best method, as Rodney mentioned, is a spray etcher. The air stones are slower and much less expensive, but do a good job of stopping undercut.

If you wish to take the high dollar road, google "masteretch".

If you wish to learn more, contact one of the numerous PCB (printed circuit board) forums on the internet. Yahoo has a good one.

Long ago, in ancient prehistory, I was in the printed circuit business, and mostly broke. Everything was home made... my warm air dryer was an old electrolux vacuum, running as a blower. $1 at the goodwill store.

Mark (older than dirt....)

Dee Gallo
09-08-2008, 8:28 PM
And when I was in art school as a printmaking major, we etched zinc and copper plates, agitating with a feather by hand, using asphaltum as a ground (blockout). Not just low tech, pre tech, I think!

-cheers, dee

Rodne Gold
09-09-2008, 2:37 AM
It's still pretty much the same as before , ancient technology , cept the commercial units have fancy pumps , washers , strippers etc.
I have a pal that does massive panels , all he uses is a elctromagnetic acid pump and a hosepipe and he has a handlanger just hose the plate down..................
If you use Edingburgh etch , the link i provided above , you dont have the same problems as with a straight ferric etchant . Ferric deposits stuff in the etched grooves that stops further etching and the addition of the citric acid stops a lot of this. The feather you used was most likely the fact that the etchant was acid based and makes bubbles where it's etching , hence the feather to remove the bubbles and not disturb the ground (resist)
The most expensive thing if you gonna build an etching tank will be the pump.....it has to handle acids and cant contain metal components where the ferric or etch comes into contact with it.

David Fairfield
09-09-2008, 10:36 AM
Well while we're on the topic, does anyone know of any metal etching forums comparible to this laser engravers one ?

The instructables website I posted earlier has some interesting looking videos of metal etching, haven't watched 'em yet.

Dave