Full Version: Acid etching / photo etching/ Brass/ Stainless steel

From: Peter [#1] 14 Apr 2005To: ALL

How do I set up to begin acid etching brass/ stainless steel ? How does the process work and what is required to set up ? Some engravers only acid etch over certain sizes ? why?

thanks in advance

Peter

EDITED: 1 Jun 2005 by JOHNFISH

From: Peter [#2] 15 Apr 2005To: Peter [#1] 15 Apr 2005

Acid etching….

can anyone lend us their experience ? Hows it done ? Why use it over straight mechanical engraving ?

regards

Peter

From: Rodney Gold (RODNEY_GOLD) [#3] 16 Apr 2005To: Peter [#2] 16 Apr 2005

It’s relatively easy. You use a mordant (etch) called Ferric chloride , best used heated to about 40 degrees. This is not an acid per se , but erodes brass , stainless , aluminium , copper , steel , bronze and many other metals. The concept is simple , you mask off what you dont want etched with a resist. (something that the etchant cant penetrate) There are literally 100’s of resists but we will be concerning ourselves with a few that many of us can make or use easily 1) Vinyl acts as a great resist , vinyl cut and weed what you want etched and apply to the metal The problems is with fine detial , you can only go as far as you can weed. 2) Polyester vinyl applied to the plate and lasered , IE use the laser to vaporise where you want to etch. The problem is there is always a residue and you have to sandblast prior to etching to get naked metal , slow , but great detail achievable , excellent for one offs. 3) Screening with acid resist inks (Coates has em) ideal for production , great resolution achievable , downside is that screen is needed and a possy/negative too. This is by far the best solution for high volume!! 4) Laminating with a dry film uv sensitive resist and then exposing using a positive or negative and washing out the unexposed bits. Pricey , but exceptional detial can be got , more than any other way.Need a laminator , must be done under special lighting , possy/negative needed . I could go into more detail for any of these and other methods , however I will just list some points to be aware of.

1) Metals have to be scrupulously clean to etch correctly , even touching with a finger prior to dipping into the etchant will leve a finger mark

Rule no 1 – clean the plate with a scotchpad or some acid rinse or whateve prior to putting on resist . Make sure the metal is clean after as well. any deposits on the bare sections will be fatal!!

2) The plate must be swished around in the heated ferric (avaialble from just about any chemical supply house in liquid form ready to use) and should be placed face down as bye products of the etch will settle in the etched surface and hinder further etching.

3) ALL areas of the plate MUST be covered apart from the part to be etched Special care has to be take on areas like edges and corners. You can use many things to block off the plate , from vinyl to varnish , paint etc. be aware if etch seeps in anywhere , you are buggered. Check the part to be etched for any problems too , like pinholes or small areas of rsist that are damaged etc. Nail varnish normally works to repair these. If using vinyl see that there are no edges lifting etc , best to roller the vinyl on the plate

4) Ferric stains fingers and clothes , will eat the wifes sink and is not healthy to ingest or get into eyes , wear safety clothing.

5) A pyrex dish is a good starting etching tank A platic cats litter box is too and a baby bath tub for even bigger. Aquarium heater are great to keep temps up – you get 300 watt ones , just be careful with electricity and they get REAL hot.

6) Aluminium needs dilute etch , dilute 1:1 with water – if you dont the reaction goes exothermic and runs away with fumes and foam and all sorts of stuff all over. Anodised aluminium should be etched with caustic soda (nasty stuff) and not ferric .

7) keep different metals to diff tanks , when the etch gets a dirty olive colour and is syrupy of is not working well , dispose of it safely , in a container and give back to the chemical house , do not pour it down a drain , sewer or into the ground , be responsible!!

8) it can take some time to etch deep enough to do lets say a paint fill in stainless steel, Ideally you need to mist spray hot ferric onto stainless or other metals , this can give you removal rates as fast as 1/10th mm per minute , but its really expensive to get the pumps and hardware to do so. The problem is this , the etch undercuts , IE it eats in under the resist and often fine stuff goes with it , the longer its in the etch the worse this becomes. Check often to see your resist is still intact – wear rubber gloves and eye stuff for splashes etc You can rinse the plate in cold running water , inspect and put back into the etch.

9) Do all this in a well vented place

10) If using a laser on polyester based vinyl , rather vector cut large areas and raster only fine detaIl , saves a ton of time.

11) The is a product called press and peel which you put thru a laser printer , develop and iron onto the metal , similar to the dry photoresist but easier to use – google it if you are interested , I think it’s press ‘n peel.

You can start etching easily at home , tho if you get more serious , you need decent stuff.

As I think of more things , I’ll add to the thread and answer any questions. I built my own etching plant and do a lot of it so am familiar with most things Hope this helps you Regards Rodney

From: Harvey only (HARVEY-ONLY) [#4] 16 Apr 2005To: Rodney Gold (RODNEY_GOLD) [#3] 16 Apr 2005

I used to etch printed circuit boards for prototypes.

You seem to have covered the subject end to end with one minor exception.

On PC boards the trace was extended beyond the card edge and made solid. They were put in the solution vertically, with an alligator clip on the solid edge, (held above the liquid line), to a power supply. The other end of the power supply went to a carbon rod which accumulated copper. (The rod from the center of a carbon/zinc D battery worked great. You just had to remember that the last thing to go into the solution was the carbon rod, and it also had to be the first thing out.) I do not remember the voltage, or even the polarity, but it halved the etch time and seemed to extend the life of the ferric chloride a bit by removing the copper that would usually go into solution. It also required good agitation due to the speed of the etch.

From: Rodney Gold (RODNEY_GOLD) [#5] 16 Apr 2005To: Harvey only (HARVEY-ONLY) [#4] 16 Apr 2005

Hiya There is another way to extend etch times and stop etch byproducts hampering the etch as well as making it far more predictable and that is to make whats called an edinburgh etch which contains a small percentage of Citric acid – needs very precise baume measurments of the ferric and needs to be mixed accurately

Adding to the thread various other etchants can be used , for example cromic acid on brass gives a marvellous effect , the etched portions become frosted. Heres a link to a home etching set up and operation if anyone is interested , it’s a little too complex but it also gives a nice parts list for usa ppl to set up an etching tank. http://www.prototrains.com/index.html#equipment One thing I didnt add is that a laser is VERY well equipped to process curved or irregular surfaces and even cylindrical ones. Also , if you really want to do big stuff (like huge panels) then you make yourself a pvc type urinal thing (use guttering) and prop the panel up in it , then using an isolated pump and a hose , actually HOSE the thing down with hot ferric. The pumps we use are pretty high volume high pressure 3 phase magentic coupled ones specifically meant for acid pumping and highly corrosive stuff. The are VERY expensive , I think ours cost me more than $1000. Anyway , it’s pretty easy to do at home without spending more than $20 or so , I think radio shack carry the etch (something about circuit boards – im not in the usa) and get a piece of brass , use a scotchpad on it to get it rough , take a permanent marker and colour it in , scratch a design , etch it , and wipe off with spirits , the perm mark ink will act as a resist. Furthermore to resists , we often just spray painted the plate with a primer and overcoat and used the laser to zap the paint , we cleaned any residue with a gentle rubbing of handy andy after lasering and before etching. Often for us it’s hard to decide what to etch or just plain engrave. Often if artwork is good , albeit it takes longer to complete , its often a quicker process to engrave. If you are taking away large surfaces or need ultra fine detail , then etch. One of the advantages of etching is that you can use raster pictures or graphics , often impossible with engraving. I’ll add more as I think of it 😉

From: Rodney Gold (RODNEY_GOLD) [#6] 16 Apr 2005To: Rodney Gold (RODNEY_GOLD) [#5] 16 Apr 2005

I just remembered something , letraset letters , you know those ones that rub off , make a wonderful resist , it you use them all the letters stand out as you rubbed em on. Another thing , always compensate for the undercutting , IE the tendancy to thin fine relief more toward the base the deeper you etch. So teeny letters that stand out need to be thickened up , do this compensation when lasering a resist too , the fine lasered lines will be thicker than you expect.

From: Peter [#7] 25 May 2005To: Rodney Gold (RODNEY_GOLD) [#6] 25 May 2005

The Question …..!

How do we set up and what equipment do we use to set up a viable etching system in our workshop.

Where are the measurable advantages of Etching over engraving?

regards

Peter

From: Rodney Gold (RODNEY_GOLD) [#8] 25 May 2005To: 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 2005To: Rodney Gold (RODNEY_GOLD) [#8] 25 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: 25 May 2005 by PETER

From: Stunt Engraver (DGL) [#10] 26 May 2005To: 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 2005To: 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 2005To: 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