Sometimes when you remove a stencil, a faint outline of the image will remain in the screen. This is called a “ghost” image (or alternately “haze”), and it can happen for a couple of different reasons. Ghosts can occur when leftover ink from a previous print run gets trapped in the nooks and crannies of your screen mesh, or when underexposed emulsion reacts with your screen cleaning chemicals. Usually ghost images are relatively harmless, aside from possibly complicating your registration a bit on your next job. However, a more serious ghost image can actually block openings in the mesh and keep ink from passing through during the print stroke, creating pinholes.
So you’ve noticed some troublesome ghosts plaguing your screens – what to do about them? Before you start questioning whether this screen printing job is worth eleven-five a year, let’s talk about a process called “dehazing”: the removal (i.e., busting) of ghost images.
There’s a wide variety of chemicals, called haze removers,, you can use during screen reclamation to eliminate ghosting in your mesh. Haze removers can be caustic, so be careful to closely follow the instructions provided and take all recommended safety precautions to avoid harming your screens – and yourself! It’s always a good idea to use chemicals in your screen printing shop that are as environmentally friendly as possible without sacrificing effectiveness, so be on the lookout for greener options.
Dehazing is a simple process. Just wet down your screen and apply your haze remover according to its instructions, then scrub away the stain taking care not to damage the mesh. Let the screen sit for awhile to give the haze remover a chance to work, but not too long – some haze removers can eat away at the glue holding the mesh to the screen or even the mesh itself, potentially damaging your screen beyond repair. Once the haze remover has had a few minutes to do its thing, rinse the screen. You may have to repeat the process for particularly pesky stains.
Keep in mind you don’t always have to go out of your way to remove ghost images; they’re really only a problem if they’re negatively affecting your print quality or making your registration unnecessarily difficult. Even better than removing ghosts after they materialize, there are steps you can take to prevent them from showing up in the first place:
With a little bit of effort and the right supplies, you can exorcise your ghosts easily and keep your screens in perfect shape for every print run.
Looking for some more tips on how to clean and expose your screens properly to avoid screen printing issues? Check out these blog posts: