How to use “Puretch” high resolution photopolymer etch resist for making pattern plates and etching brass, copper, bronze, sterling and metal clays.
By: Nancy Hamilton 08/01/09 and 8/21/11.
The product I use to transfer images to metal for etching is called 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. Here are Cape Fear’s instructions for the paper. Remember that their instructions are for etching plates used for printing. We, as jewelers, are using this product in a slightly different manner. Because of the use difference, the instructions will differ slightly. The instructions I give below, are based on my experience with this product.
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.
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 photopolmer 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 or bases. The areas left exposed (the white or “clear” areas) get exposed and harden. This hardened paper stays on the plate during the etching and keeps the metal smooth and untouched. 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.
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.
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, 130mm (approx. 5”) is as wide as you should make it. The width of your metal is determined by the roll-able area of your rolling mill and the size of your exposure unit. Length is limited by the size of your exposure unit.
Clean the metal (see my page titled: Cleaning Metal found under the Materials tab/Wire and Sheet Metal/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 more earth/human unfriendly, product. Some recommend cleaning with TSP but it is a phosphate based product that is not environmentally sound. 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.
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. 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 Brooder Clamp Lights or just plain (clamp lights) and outfit them with CFL (compact fluorescent light bulbs) yellow bug light bulbs. I have two in my studio and that is sufficient light for working.
Puretch application. 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.
Exposure. 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.
You need a timer that shows seconds. I use a kitchen timer.
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 but, we have found that 30 seconds is plenty with the Ocious unit and 1 minute with my homemade unit. See information below about exposure solutions. When the time is up, turn off the UV light source.
Exposure box. You need a UV light source. The sun works but is VERY unpredictable. A 50 halogen light will work – a little better control than the sun, longer exposure, not as even an exposure as with the following sources. For absolute control you need a black light box or a nail drying light. YCC Ocious’s 9 watt nail curing UV lamp (http://www.sallybeauty.com/Professional-Curing-UV-Lamp/SBS-128400,default,pd.html?cgid=Nail06) will work for smaller pieces. I built my own exposure box with two fluorescent type black lights already in the light fixture, cut up some pine shelving – 8” wide pieces for the four sides and a12” wide board for the top and bottom – $15.00, covered all interior spaces with tin foil that was glued down with white glue, drilled a hole in the end to run the 2 cords through and hooked them up to a plug strip ($3.00) with an on/off switch. I’m almost positive that “grow lights” for indoor plant growing will also work. The “door” and the bottom are simply loose boards with tin foil on the inside. I prop the door shut with whatever is available. Here are two pictures of my homemade unit:
The “door” is on top of the box.
This shows the “floor” that is not attached. The box is basically a squared off “C” shape with a back and a non-attached floor and door. Lazy girl carpentry at its best.
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 work well enough for me.
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, these sites offer excellent information on exposure equipment and other related information.
Developing. 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.
Removal. 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!