I wanted to document what I've learnt recently when it comes to doing photo-etching at home as there's a lack of information online when it comes to timings particularly when you don't have a specialised UV exposure unit! Photo-etching isn't for the faint hearted and can be a pain if you don't follow each step to the letter. If you want an introduction to printmaking, Printmaking A Complete Guide to Materials & Process by Bill Fick is an excellent read.
To prepare stencil:
- Open digital image (JPEG) in Adobe Photoshop. If in colour, Image > Adjustments and select either, Desaturate or Black & White, then fine tune the image. You will need an image of medium-high contrast with good areas of black and white.
- In photo-etching, you will need to add a fine grain to the plate for the ink to adhere, otherwise it will simply wipe away clean in areas that should be dark. To do this, usually you would add an aquatint or use an aquatint screen but an easier method is by Bitmapping your image. Firstly, Image > Mode > Grayscale, then Image > Mode > Bitmap. It will request a resolution output and generally if your image input is 240-300 dpi, you will need to set it lower ie. 200 dpi range then select Method - I use diffusion dither but it's up to your aesthetic preference! Print bitmapped image as grayscale onto acetate or transparency (ink jet or laser is fine).
**Advanced stencil preparation:
You can prepare a duotone photo-etch (printing with two plates) by preparing the same image with two outcomes. One stencil is lighter with small areas of detail (top layer) and the other darker with large areas of detail (base layer).
Or, for a four colour separation CMYK (printing with four plates) you will need to prepare you stencil by separating the colour channels of your image. Firstly, go to Image > Mode > CMYK Color then, go to the Channels panel (if not shown, check on the Windows tab to see if ticked). Alter Brightness & Contrast, as well as Levels for each colour channel in the Image > Adjustments menu. You will need to ensure that each colour channel has a medium-high contrast. To separate channels into files, select ∨≡ button on Channels panel and select Split Channels.
Continue to bitmapping.
- Traditionally, zinc or copper plates are used in intaglio processes. Whilst copper is easier to work with, it's a tad expensive.To prepare a plate you will need to do the following:
- File and bevel edges to 45 degrees and soften corners.
- Remove protective film and clean plate with white spirit.
- Degrease plate. Normally, you would use ammonia and whiting powder some printmakers use soy sauce, concentrated washing up liquid, white vinegar and bicarbonate of soda etc. This is an important step as it helps with the adhesion of emulsion on the plate. Note: DO NOT TOUCH THE PLATE ONCE DEGREASED (clean gloves are recommended).
- Another good measure, is to rinse plate with distilled or deionised water as it reduces potential water marks. Remove excess water with clean cloth and finish with a blow dryer.
- There are two mediums that you can use, photoresist film and photoresist emulsion. They both have their pros and cons, personally I prefer the emulsion but if you want to reuse the plate then I would recommend film.
- Film: Cut film slightly larger than the plate. Spray plate with a fine water mist and remove backing sheet on film (you may need tweezers) then lay on top of degreased plate. You will need to run plate and film in a printing press to adhere film. Afterwards, remove protective layer on film and trim down to fit plate. This needs to be placed in an oven for at least 20 minutes to cure or left overnight.
- Emulsion: Using a palette knife, mix some emulsion with 1-2 drops of reducer. Roll on emulsion until there is an even coverage and a semi-matte finish. Place in dryer for 20 minutes and allow to cool.
To expose a plate, I used a UV nail lamp from eBay. You can figure out your ideal exposure times with a step test as they can change depending on your stencil. For an image like below, it took a 45 second exposure. For a lighter stencil, reduce the time and a darker stencil, lengthen the time. **Note: UV lamp stands 3.5inches away from stencil.
I use an old photo frame for exposure by sandwiching the backing board, plate, stencil (reversed) and glass clipped together.
Once exposed, develop plate in a solution of bicarbonate of soda (1-2tbsp) and water (1 litre). If development is slow, add a little more bicarbonate of soda. It can take time to develop but continue agitating the tray and gently wipe the surface of the plate with a sponge or brush. *Note: emulsion is fragile
After development, rinse and remove excess water. Place underneath UV lamp for another exposure to harden emulsion. You're ready to etch.