Full Version: Acid etching / photo etching/ Brass/ Stainless steel
From: Rodney Gold (RODNEY_GOLD) [#8]
25 May 2005
To: Peter [#7] 25 May 2005
Its actually real easy to set up a LIMITED etching operation.
There are big advantages to etching in that you can get very fine detail which you cant in engraving as well as the fact that removal of large areas of material can be achieved VERY quickly and that you can do stuff you couldnt possibly engrave succesfully (like photos)
The principle is that you coat a plate with a resist , ablate/remove the resist where you want to etch and use a mordant (the etch medium) to remove the material.
All you need to start is a few pyrex / plastic dishes , a basting brush with no metal parts and some ferric chloride and a platic set of tongs (to remove the plate and inspect) and possible an aquarium eater
Lets start with the mordant (etch). You have a large choice in what to use , various acids and acid mixtures , but the safest and most versatile stuff to use is ferric chloride which just about any chemical supply house has in either liquid or crystal form. Buy the liquid - the concentration of Ferric in solution is important and needs to be 36-38 baume - don't worry about this , the supply house should have it mixed to the right concentration.
Its the same stuff used to make circuit boards and I beleive Radio shack stock it ?
Other mordants like hydrochloric , nitric acid and so forth can be used but are dangerous. Ferric is not an acid per se , but must not be ingested or come into contact with skin or get into your eyes , so whatever you do , protective clothing is a must. DO NOT use it on the kitchen sink , your wife will kill you when she sees how the spilled drops have eaten away the SS.
Ideally you want the ferric to be heated to about 40 degrees c and even better is to spray it in a fine mist on the part to me etched.
However heating is possible , but unless you go to some trouble , spraying isnt.
The way to heat it at home is 2 fold , either get a bigger dish than the one you are going to use for etching and fill with hot water and put the etch dish in that or get an aquarium heater and put that in the dish used for etching
Now to the resist. Here the choices are truly extensive , you can use beeswax , paint , vinyls etc etc. For us with lasers , a polyester based vinyl is best (shiny gold and silver are mostly polyester) .
The biggest problem one has with a resist is the fact that heat and undercutting tends to lift the resist on the surface of the plate and etch seeps in where you dont want it. Undercutting is the fact that when the etch works and goes deep , it tends to not etch straight down but rather makes an etched line wider at the bottom .
On that note , once you have finished lasering etc , you MUST make sure the plate is sealed on the back and edges and EVERY place you dont want it to be eaten away. Ordinary cheap vinyl or varnish works well.
Laser thru the vinyl where you want to etch. However there is a little fly in the ointment. When you either ablate paint or vinyl , there is a residue left on the metal and to etch well , the metal has to be scrupulously clean of any oils (like fingerprints) or residues.
If you have a sand blaster , a quick blast after lasering removes residue , oxidation and gunk , if not , a soft abraisive household cleaner like Handy Andy used with a soft toothbrush on the exposed areas is needed. Inspect the plate closely after cleaning , ANY gunk will not etch properley!!!!!
The polyester based vinyls have pretty aggresive adhesives , so using the cleaner wont dislodge small pieces like the middles of A's. However it WILL be more difficult to remove the resist after etching (A heat gun works well)
The problem with etching is that the by-products of etching settle to the bottom of the etched area whilst its being etched and stop further etching , hence the basting brush which you swish over the plate while it's etching. Etching face down is an option too.
Once the plate is fully prepared , dip into the etchant and let it do its stuf , periodically swishing the etch over the plate and using the plastic tongs to take it out , inspecting for depth. Once deep enough , remove the plate , wash VERY well with water and a bit of soap and remove the resist and hey presto , a Pro style etched plate.
If you are doing stainless at home , it could take as long as 45 minutes to get a deep enough etch for paint filling. Brass/copper/bronze is a lot quicker. Be VERY carefull etching aluminium , the Ferric is a little to strong and the stuff goes exothermic and starts foaming and fuming , a 50% dilute mix is better and anodised ally will not etch. Most use Caustic soda for aluminium , but this is pretty nasty stuff.
In terms of production , etching is hugely faster than engraving. Commercially based etchers screen plates with acid resist inks or a dry resist and use UV to expose the plate to a positive or negative and have semi automated hot etch spray systems that can remove .1mm of stainless per minute and are capable of etching both sides of a stainless plate. It takes almost no time to screen or expose/develop.
As I said , the detail you can get is incredible , especially with a laser and you have no concerns about tool wear or milling marks or bit widths , nose cones that ghost etc that you would have with a engraving machine. Added to that is the fact that you can do curved stuff with a laser.
The bottom surface of etched plates is way smoother and consistent than engraving and considering etching is a non contact type milling , the metals do not get stressed or heated.
Its also easy to do without a laser as you get a photo sensitive (UV light) resist that can be applied to a plate , you can then use a laser printer to print the black image on vellum , tracing paper or laser transparencys , put it on the resist and expose to UV (the sun is a great uv source) , develop and etch. You can even draw on a plate with a permanent marker like a Sharpie and use the marks as a resit. If you have a vinyl cutter you can cut and weed and apply and etch. You get a resist called press n peel which you run stright thru a laser and then can
From: Peter [#9]
25 May 2005
To: Rodney Gold (RODNEY_GOLD) [#8] 26 May 2005
"You can also quite easily build a spray etcher using irrigation nozzles , a large polyprop tank , a decoupled acid pump and a titanium heating element (Im not going into that here)
Hope this helps
any questions , just fire away!!"
Rodney, your help to everyone world wide is simply beyond description, heres my suggestion..start a magazine, write a book, have a video instruction series, Go on a guest speaker circuit in the USA.....Lord knows, there's 280 million of them and they would beat a path to your door .......
I have a question and I'll fire away.......How do you build that thingamajig you described above..................
regards
Peter
EDITED: 26 May 2005 by PETER
From: Stunt Engraver (DGL) [#10]
26 May 2005
To: Rodney Gold (RODNEY_GOLD) [#8] 26 May 2005
Rodney,
First, I agree with Peter. We'd love to see a DVD, book or some form of tangible instructional piece, on some of the many "everyman" approaches to processes which are generally performed by semi-expensive equipment.
Extremely informative post!
I have a question:
When paint filling an acid etched piece, do you leave the mask on, as a means of easier cleanup?
From: Harvey only (HARVEY-ONLY) [#11]
26 May 2005
To: Rodney Gold (RODNEY_GOLD) [#8] 26 May 2005
As usual you have gone the distance and then some.
Your willingness to share the extreme details of the business in aspects that most of us would not have attempted is amazing.
Thank you.
From: GBengraver [#12]
26 May 2005
To: Rodney Gold (RODNEY_GOLD) [#8] 26 May 2005
Rodney,
How do you deal with the highly polluting waste by products?
You can't just pour that kind of stuff down the drain.
Just a thought.
Greg