Recently I was approached with requests to etch two photographs, one on glass, the other on stone; both were memorial pieces, one for a human, the other for a canine champion. I thought this would be a good opportunity to come back to some of the basics of etching photographs; we get many questions about this and, of course, teach a special workshop on these techniques.

One of the first things we always have to clear up is the belief that if you use something called photo resist, it must mean that you use it to etch photographs. We often explain that calling it photo resist simply means that the image on the resist is created by a photo process (which involves light exposure), but is not necessarily an image of a photograph but rather black and white artwork.

Photo resist can easily reproduce designs for etching that have very fine detail, and it can be used to create the exact same design any number of times. Using photo resists to etch photographs is a bit more involved and has a steeper learning curve. There are three major reasons for this.

First, to reproduce a photograph, you have to manipulate the image to create what is called a halftone of the photograph. Second, you have to have a photo resist that is capable of handling the unique nature of the processed halftone artwork. Third, you have to be able to blast the image.

Throughout the past few years, photo resists have been improved to the point where they can handle halftones, and at the same time, graphic software has been improved to make it much more user friendly than ever before when creating halftones. Now it has become possible for most people to etch photographs with the right knowledge and the right materials. To get good at it will still take some time and lots of practice. Here are some of the basics.

Here you see the process of converting a color photograph into a black & white photo and then into a halftone for etching.

Manipulating The Photograph

Since surface etching creates a basic black and white image through blasted and un-blasted areas, we must start with a black and white photo or convert a color photo to black and white in the computer. A black and white photograph is an image composed of different shades of gray, ranging in color all the way from black to white. Since etched glass only has two apparent color values to it—white (the etched areas) and black or dark (the clear areas)—gray tones have to be simulated.

In printing, the simulation of gray tones in a photo is done by a process called halftoning, or creating a pattern of black dots on white paper. When viewed from a distance, your brain merges these dots to see a color of gray. More dots, closer together, represents the darker gray areas of a photo. Less dots, further apart, represents the lighter areas.

In etching a photo, the effect is exactly the reverse. Instead of printing black ink on white paper, you etch white background areas around clear dots, which look black in the finished piece, using exactly the same type of halftone image used in printing.

To prepare your chosen photo, you have to get it into your computer, by scanning it or by importing a digital photo from your camera. Then, using image-manipulation software like Adobe Photoshop or Corel PhotoPaint, you convert it from color to black and white. Using the same software, you can generally improve the photo a great deal by doing things like improving the contrast level, blurring or removing the background. If you want to add etched text to the photo, you can do a basic layout with the above-mentioned software or a more sophisticated job with related software like Adobe Illustrator or CorelDraw.

When you have come up with the best version of the photo, you need to put it through the halftone process. Both Photoshop and PhotoPaint can halftone a photo. We use both programs, on both Mac and PC platforms, but our art department definitely prefers Photoshop. We get better results from this program, but it does take time to master. If you are a graphics beginner and if you have PhotoPaint, you can get a plug-in program from Ikonics that automates the creation of halftones. This program, called Half-Wiz, can create a halftone for you in just 2-3 clicks. You do sacrifice some control over the results in return for this ease of use, though.

In the halftoning process, you need to learn to change any black areas of the photo to 80% to 85% gray and any pure white areas to a maximum of 80% to 85% white, to improve etching results. You will also need to select how large the dots will be. The smaller the dots, the better the etched photo will look, but the more difficult it will be to etch, and vice versa. Most people start out at a 35 line screen, which is fairly coarse, and later move up to 45, 55 or even 65, which are much finer but also much more difficult to blast. (All of these settings are considered coarse by the printing industry, which uses a 133 line screen to print images in magazines.) In the software, these settings are considered the screen frequency.

You will also need to set the screen angle, which is the angle of the line along which each row of dots is arranged. Avoid 0 degrees or 90 degrees, since the human eye will see the dots more easily along a vertical or horizontal line. Start at 45 degrees, and print a sample. If you see a strange pattern of grid lines in the background of your halftone which was not present in your photo, you are getting a moiré pattern (pronounced mo-ray). This pattern will definitely etch in your glass, and is very undesirable. To get rid of it, change your screen angle by 2 1/2 degree increments below and/or above 45 degrees until your test printout no longer shows a moiré , then print out the final artwork. Use either the architectural drafting film (for laser printers) or waterproof inkjet film (for inkjet printers) made especially for photo resist to get the best results.

You are now ready to expose the resist and blast the image onto the glass.

Creating And Using The Photo Resist

If you have ever used photo resist before, you know it consists of a light-sensitive emulsion coated onto a thin carrier sheet of Mylar to make a film. Most photo resists are processed with water, but the one we use for etching photos is dry processed, without water. With water-processed resist, the basic resist is water soluble. But the areas of the emulsion that are exposed to light become insoluble. In order to produce a resist with a blastable design on it, you print out your design onto a translucent piece of film, lay it onto the resist and expose it to ultraviolet light. The area of the resist under the black printout stays water soluble and washes away when washed with a spray of water, while the area that was exposed to light remains on the glass to protect it during the blasting process. When washing out a halftone, you have to use a high-power spray washer (the Trigger Jet won’t do), and you have to be very careful not to wash off some of the tiny dots, ruining the resist.

With the dry-processed resist, you simply expose the resist with the design on it, apply it to the glass and blast. This eliminates the chances of ruining the resist by over-washing, since you don’t wash at all. With both types of resist, you still have the chance of ruining the glass by over-blasting.

The dry-processed resist we use is RapidMaskHD™ by Ikonics, the only dry-processed resist on the market. The resist is only 2 mils thick, and the exposure time is 1 1/2 to 2 minutes with the standard Letralite. It is very tolerant of overexposure, so we prefer to get close to the 2 minute mark.

After exposure, you remove the protective slip sheet on the resist, exposing the adhesive. Since it is very important to get the resist where you want it and without air bubbles, we use the wet-application method. Simply spray the glass/stone and the adhesive side of the resist with a fine mist of water with a drop of dishwashing detergent and lay the resist down on the glass, adhesive side down. Move the resist around until the positioning is correct. Then squeegee all the water out, starting in the middle and working to the edges, always making sure not to shift the resist. Leave the resist on the glass/stone for a few minutes to develop better adhesion, then remove the Mylar cover sheet. After removing the cover sheet, we prefer to let the resist dry out a bit and develop even more adhesion before doing anything else. This generally takes only 10 to 15 minutes. Then tape the edges of the resist and any exposed areas of glass you don’t want to get blasted.

Put the glass/stone into your blasting cabinet and set your pressure blaster to 20 to 25 psi on glass or 30 to 35 psi on stone. Hold the nozzle about 6 inches from the surface and make even sweeps of the nozzle back and forth. Start at the top and work your way down, overlapping each pass at least 50% each time you go across. Since the exposed resist has changed from its light green color to a medium blue, it should be easy to tell when you are finished. Should is the operative word here, because in reality, it can be very difficult to tell just when to stop. If you stop too soon and remove the resist, there will be large un-etched areas of the photo, which will ruin the glass. If you go too long, you will start blasting away the tiny dots which will ruin the image, and consequently the glass as well. It is easier to see what you are doing on glass, since you can see through it; on stone you have to look much closer to be able to see the change on the surface. That is where the practice part comes into play: only practice will give you the feeling of when to stop at the right time.

The image manipulation and the exposure process are more closely related to the science of this technique; the actual blasting is definitely more of an art. It can be done and done successfully, but it takes a fine touch and lots of practice on inexpensive scrap glass. We usually blast a couple of sample sections of the image before attempting the final piece.

Keep in mind that if you have a halftone of 35 lines per inch or less, you can use 180-grit abrasive. However, a halftone of 45 lines or more should only be blasted with 220-grit abrasive or finer. While it is theoretically possible to etch a halftone of 65 lines, this is very difficult and depends not only on the skill of the person blasting but also on the actual grey tones in the photo.

Etched photos can open up a new, high-end market for you in many different types of custom products. Since so few shops offer products with photos etched on them, you should be able to command a very good premium for these items. And as mentioned before, in addition to glass, with a little practice, you can also learn to etch photos on ceramic, stone and even metal.
 

© Ruth L Dobbins 2011