What Are Ghost Images?
A ghost image is a stain in the mesh of the screen. This can occur from either the ink or emulsion used to create the image. Most printers experience both types of ghost image. In both cases, there can be several reasons for the ghosting.
Partially underexposed emulsion is a very common cause for ghost images. When put in contact with certain clean up chemicals, underexposed emulsion can become locked into the knuckles of the mesh, making it very difficult to remove. Be aware of what chemicals you’re using, and always try to avoid underexposing screens. Although a slightly underexposed screen can be used without any apparent problem, come reclaim time, you may find yourself with a stubbornly locked screen.
Aside from an underexposed screen, there are a number of other causes for ghost images. If your screen has low tension, you’ll need to set your off contact higher, which means you’ll end up using excessive pressure to get a good print. This can trap pigments in the mesh. The use of abraders during your screen prep can cause scratches in the surface of the mesh that creates areas for pigments to settle. Also, very similarly to underexposed emulsion, if you do not dry your screen properly prior to coating, you can end up with an emulsion ghosting.
A few other tips you can follow for avoiding ghosting include:
- Make sure your screen is properly exposed. Use an exposure calculator if you’re not sure about your exposure time. After you’ve rinsed your image out, and your screen is technically ready to print with, put it back on your exposure unit for 3x-6x your original exposure time! This post exposure will finish hardening the emulsion that is left after you rinse the image out.
- Clean BOTH sides of your screen during clean up. If you clean on just one side, you’re pushing all of the chemicals, ink, and emulsion to one side of the screen and this can cause problems.
- Avoid “hot” solvents, such as lacquer thinners. These can react poorly with emulsion and lock it into your screen.
- Try not to leave your ink in-screen longer than necessary, especially with solvent or water based inks. When you’re done printing, scrape out the ink and clean up the screen.
- Low screen tension? Either get your screens re-meshed, or look into other screens! Low tension in screens can cause more issues than just ghost images, so it’s something you’ll want to keep an eye on.
- Make sure your screens are dry, both before and after coating. Have a set up where you can set your screens up to dry. Box fans are a great, cheap way to get some air flow on your screens, which can speed and guarantee proper drying.
How Do You Get Rid of Them?
There are several haze removal products out there that can help with leftover ghost images. Please keep in mind that haze removers tend to be pretty harsh chemicals, so you want to be careful while using them. Certain industrial strength haze removers can eat through mesh if left on a screen too long, so don’t step away while dealing with ghost images. Whenever using a dehazer, make sure you follow the directions for it precisely.
We recommend the use of our Sgreen Stuff Dehazer and Degreaser. Sgreen Stuff does the job of two chemicals, both a dehazer and a degreaser. It uses a unique pumice additive that cleans the mesh of stains, and oil and contaminants at the same time, leaving you with a fully reclaimed and ready to use screen while being more environmentally friendly and easy on the nose.
Hazes, or ghost images, can happen to the best of us, but by paying attention to your stencil preparation, exposure process, and what chemicals you’re using, you can avoid the worst of them.