The ink stains that sometimes show up in your screen mesh shouldn’t be accepted as a regular byproduct of the day-to-day. If all of your screens have these stains known as ghost images, there’s a step or two in your preparation or cleanup practices that must be fixed. Rather than looking for ways to exorcise those screen-bound spirits after the fact, try these tips to eliminate them much earlier in the printing process.

Stop underexposing your screen mesh: Underexposing your screens can be the first cause of ghost images. Certain chemicals used for cleanup after printing can cause the underexposed emulsion to harden on the mesh surface and result in a ghost image.

Ghost images in your screens are commonly a result of an erroneous step in the process that can be corrected. Photo courtesy: Workhorse Products

The solution is to post-expose your screens after washout. Once a screen has been exposed and dried, no amount of additional exposure will damage that screen and stencil. If you’ve ever driven past a screen-printing shop and seen screens lining a wall facing the sun, that screen printer is post-exposing to harden the emulsion. You can do the same, either with an outside window or your exposure unit. When you post-expose your screens, the inside (ink side) of the screen should face the light. If your screen is underexposed, the inside of the screen will have the least contact with your exposure light source and therefore need the most post-exposure.

Be sure to thoroughly dry your screens before post-exposure. The water in the image area on an underexposed screen can easily be clear emulsion rather than just water. Exposing clear emulsion will cause “glazing” of the mesh, blocking the mesh just like the rest of the emulsion on your screen.

Also, eliminate underexposure by testing your cure time. Your ink and chemical supplier can sell – or sometimes even give you – an exposure calculator. This is a film positive with a filter attached that you expose onto a screen. Select the time you think is appropriate and double that time. Expose the calculator at this double time, then look at the filtered area for the absolute best exposed image. Take the formula below that image (the decimal number times the double exposure time) and you’ll get your ideal exposure time for your equipment and shop. This should eliminate any underexposed screens on your production floor.

Clean with the right chemicals: I have a friend in the industry who always says, “It’s screen printing. Use the chemicals made for screen printing.” However, many decorators try to save a few bucks by using less expensive products, or taking the advice of self-proclaimed experts online. Using paint thinners or mineral spirits to clean plastisol ink from your screen can lock ink and emulsion into the mesh. The press wash and ink degradant chemicals your supplier offers will be gentle on the mesh and eliminate the ill effects of using the wrong chemicals for screen printing inks, emulsions and mesh.

Once you’ve completed a print job, finish up by cleaning the screen right away. Leaving ink on a screen for an extended period can cause some ghosting as well.

Use haze removers only if necessary: When you go to reuse a screen, a little ghosting shouldn’t be an issue, but most of these after-images can be removed if you choose. Though they are caustic and ideally avoided, haze removers are useful for removing ghost images. Discuss the best chemical for your needs with your local screen-print supplier and follow their directions exactly.

If you regularly see ghost images in your screens, you’re doing something wrong. Haze removers are merely Band-Aids. Instead, take proactive measures on the front end so you’ll have perfect screens you can use over and over again.

Terry Combs is a 35-plus-year veteran of the garment-printing industry and has managed production shops across the United States. He’s currently in sales and training with Equipment Zone, in Franklin Lakes, NJ, working from Scottsdale, AZ.