YouTube video from Cape Fear Press on this process. They demonstrate preparation and exposure for larger etching plates.
How to use “Puretch” HIGH RESOLUTION PHOTOPOLYMER ETCH RESIST for making pattern plates and etching brass, copper, bronze, sterling and metal clays.
The product I use to transfer images to metal for etching is called Puretch (pronounced purEtch) and it’s available at Cape Fear Press. When not using the paper, keep it in a black plastic container or the packaging it came in, in a dark space. It is VERY UV sensitive.
Images chosen should be line art – no gray areas. You can draw or use other clearly black and white imagery. If you are Photoshop savvy, you can use my tutorial: Photoshop Tutorial – Image to Line Drawing to convert your images to black and white. Cape Fear also has information on creating Half Tone Positives for Photo Etching using Puretch.
Transferring your image
Images need to be printed on transparency paper. By using transparent paper, UV rays can penetrate to the photo sensitive paper underneath. Wherever there is black ink (your printed image), the UV CAN’T penetrate. The photopolymer paper under that black ink remains unhardened and can be washed away when it is developed, leaving bare metal that can be attacked by electricity (E3 or other electrical etching system), acids, salts or bases. The areas left exposed (the white or “clear” areas) harden. This hardened paper stays on the plate during the etching and keeps the metal smooth and untouched. This is what is called a resist. The end result, after etching is that you have areas of high relief (the exposed area) and low relief (the etched areas).
Transparency paper is sold in many stores. Check your local office supply or art stores. Amazon sells 3M Color Laser Transparency paper for use in color laser printers. Use this only if you have a color laser printer. If you have an inkjet, they also sell inkjet and copier transparency papers. Be very, very careful in choosing your transparency paper as it can melt in your printer and RUIN it! Toner based black and white images are best. You can have your images photocopied. If you use an inkjet printer, be aware that the ink will run if it gets wet. During the following processes, ensure that your image stays dry. Print on the darkest setting, with the most saturation. See your printer manual for information on how to do that.
Don’t forget to flip your image – if needed. If you are roller printing, you will need to reverse the text. If you are just etching your metal, you don’t have to reverse it. You want your text to look like this for roller printing:
Ensure that the metal you are using is flat (Should not look like this picture!!!) If you have cut your sheet metal with shop sheers or a bench type, guillotine shear, ensure that the edges of the metal are not curled. If they are, use a plastic or leather mallet to hammer the edges flat. You can also place a piece of wood over your piece and hammer it that way. Anneal the metal first so that it is easier to flatten.
Cut metal to size – which means – ensure that there is enough space on the metal for your image and a border of approx. 1 mm around the entire image. (Closest inch measurement: 3/64th or decimal of .0469).
Generally, if you are etching plates for use as pattern sheets, check to see the maximum width that your rolling mill can handle. Also, you need to consider how much room you have in your exposure unit. Length is limited by the size of your exposure unit.
Clean the metal (see my page titled: Cleaning Metal) with pumice powder (order through jeweler’s supply stores) or Bon Ami, A non-toxic version of cleanser. Bar Keepers Friend (found in grocery stores – contains oxalic acid – don’t mix with other household cleaners or bleach) is another, if a slightly less than earth/human friendly, product. Puretch recommend s cleaning with TSP (in their video). Be aware that it is a phosphate based product. When using any of these cleaning products you should always wear a particulate mask (dust mask). Wear gloves with BKF and TSP. Wash hands after use.
The metal is clean if the water “sheets” off. If you see any areas where the water balls up, the metal is not clean. Handle the metal by the edges only, after cleaning. Don’t forget to wash your hands well and keep them away from other parts of your body – especially your face (very oily).
Lighting while you work
At this point you need to go UV dark. You don’t want any fluorescent, halogen, sunlight or other light source EXCEPT for yellow bug lights or a darkroom light – besides the lights in your exposure box. Amazingly enough, these lights offer plenty of visibility and protect your UV paper from being exposed. You can either have dedicated “yellow” lights or change the bulbs in existing lamps. I use those cheap lamps from the hardware store that are called Clamp Lights and outfit them with yellow bug light bulbs. I have two in my studio and that is sufficient light for working.
Applying the Puretch Paper to the Metal
Mist the clean metal with distilled water in a spray bottle (you need distilled because the minerals found in non-distilled water will “dirty” the metal). Set aside. Now, cut Puretch paper to fit over your metal, using scissors or a razor knife. The paper is coated on both sides with a protective paper. Using either a needle, pin or a razor knife, separate one layer of the paper and peel up a corner. Tear off the clear protective paper from one side only.
Place your paper, blue (recently exposed by peeling off the protective layer) side down onto the wet metal. Using your fingers and starting from the center, press and smooth out the paper working out air bubbles. You can also use a rubber squeegee to smooth out the paper. Starting from the center and working outward will ensure that the paper is completely adhered to the metal. If there are air bubbles, start over and try again. Heat metal and paper with a hair dryer for 30 seconds to a minute. Don’t overheat (180 to 200 degrees max). I’ve recently had problems with the paper adhering to the metal and along with the hairdryer part, have started leaving the paper/metal sandwich to sit overnight. That way, the surface is fully dry. It seems to be working quite well. Try this if the paper is pulling up in areas.
You will need a piece of glass that is close to the size of your metal. Tip: You can buy several inexpensive, small picture frames, in various sizes. Make a sandwich of the following items, in this order (from bottom to top):
1. A piece of chip board or cardboard. You can use the picture frame backs for this IF you take off the piece on the back that is used as a stand.
2. Either a small piece of foam or a neatly folded piece of paper towel or fabric. The idea is to have some “give” so that the glass squishes around the metal better. You want a tight fit so that shadows don’t form under the transparency.
3. Metal with Puretch paper adhered to it, facing up.
4. Black and white image, toner side down (make sure metal is dry if using an inkjet image!).
6. Clips. I angle the side clips so that it all fits into my narrow exposure box. If you use shorter clips, this may not be a problem or hey, build a wider box (which is what I should have done)!
Clip all four sides with binder clips, clothes pins, plastic or other type of quick release clips. If the clip is too tight don’t use it as it may chip or crack the glass. The goal is to have a very close fit to allow as little light as possible to enter from the sides and under the image.
A timer that measures seconds is imperative. I use a digital kitchen timer.
The Exposure Box
Exposure box.: this is to keep other light from leaking in and to create a more even, controlled lighting situation.
In the exposure box you need a UV light source. The sun works but is VERY unpredictable and difficult to control. You can purchase a professional UV exposing unit or use a 500 watt halogen spot light. You can also make your own, as I did. The types of bulbs recommended are white UV fluorescent bulbs but, I found them difficult to find, back when I was making mine. So, I used black UV fluorescent bulbs.
Amazon carries black lights as does Home Depot. You could try an LED strip light (black light only) too. I’m not sure how they would work as I haven’t tried them. Some also use black light nail dryers. TopBulb.com carries UV Fluorescents.
Maggie Bergman discusses light sources here: (http://www.silverclayart.com/ppplates-instr.htm). She recommends not using the UV black lights but the UV white lights. The black lights worked for me though.
Ensure that the exposure area in your exposure box is large enough for what you want to do.
If you make your own exposure box, try to keep the lights about 4″ from the exposure area.
My Exposure Box
Image on left is of my DIY box closed. The “door” is just a piece of tin foil lined wood that fits over the opening. The center image shows the interior. Note holes on end for plugs and tin foil interior. I used spray glue to attach the foil and a plastic squeegee to smooth it. The image on the right shows the box upside down so that you can see the three fluorescent black lights. Puretch doesn’t recommend fluorescent light but, I’ve had luck with it. Plus, the lights were cheap. I think they are for either fish tanks, Halloween or partying. My finished box length is 24″ overall.
Using the Exposure Box
Place the piece into the exposure unit, shut the door or close the cover and turn on the unit and then the timer. You will need to experiment in order to determine the correct time. It depends on the type of exposure equipment you use. With my little box, it takes about 1 minute. If you are using the 500 watt bulb with no box, it can take 5 minutes or more. See Maggie Bergman’s information, below, on exposure solutions.
When the time is up, turn off the UV light source.
Developing the image
The following information is a direct quote from Cape Fear Press (http://www.capefearpress.com/). “DEVELOPER The developer is an aqueous solution of 1% sodium carbonate. Weigh 10g of soda ash and dissolve in a small amount of hot water, then add room temperature water to make 1 Litre. OR using a liquid medicine measurer, 1 1/8 fluid oz. of powder will make 1 gallon of developer. A tub of 100% sodium carbonate or soda ash can be bought at a swimming pool supply store very cheaply.”
Remove the clips, a take out the metal with the now developed image. You should see a ghost of the image on the metal. Lay a piece of tape across one of the sides and pull the top layer of clear protective paper off. (Be careful to not pull up the blue paper underneath.) Don’t forget to do this or your image will NEVER develop! If the paper isn’t removed, the blue paper is never exposed to the developer. I speak from experience here!
Put on gloves. Pour the developer into a container large enough to accommodate the metal. Set your timer to 1 minute. Place the metal in the developer and let it sit for a few seconds. Using either an OLD toothbrush or the scratchy, plastic side of a sponge, gently rub the surface of the metal. You will begin to see places where the metal shows through and the paper has been removed. The metal will be a light purple where the resist is. Don’t leave in the developer too long – you could destroy your image.
Let sit for a few more seconds and when the timer goes off, remove metal. If you have hard water, just rinse in the sink. If you have soft water, rinse with diluted vinegar (3 parts water to 1 part vinegar) – white wine or cider – then rinse with clear water.
Dry with the hairdryer – not too hot! Place the piece back into the exposure box, set timer for 5 or 6 minutes. What you are doing here is hardening and setting the resist (the photopolymer paper). The resist, the area which won’t etch, will be a darker purple. The other areas will show metal as these are the exposed areas and what will be etched. I usually let the plates sit for a while (half hour or so) in my studio, with regular lighting, to harden up even more. Just to be sure! If the resist isn’t fully cured the image can lift during etching. The plates are now ready for whatever etching medium you choose.
After etching, place the etched plate into the developer solution for anywhere from a few minutes to overnight. Clean remaining purple film off with a scrubby sponge or soft brass brush. If the paper is not coming off, leave the plate in the developer longer. Good luck and happy etching. I’ll discuss etching techniques soon!
Here’s Maggie Bergman’s article on How to Make Photopolmer Plates at Silver Clay Art.com. Remember that this information is for photopolymer plates NOT for Puretch but, this site offers excellent information on exposure equipment and other related information.