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Ghost Image

Ghost Images in Screen Printing: Cause and Prevention

Rick Roth is president of Pawtucket, R.I.-based Mirror Image. In recent years, his business has taken home numerous Golden Image awards in various categories, as well as top honors in the industry media's various printing competitions.

When sitting around the campfire, there’s nothing like a good ghost story to scare the heck out of you. Well, gather round the flames of your gas dryer and let’s spin a tale that will make a screen printer’s hair stand up on end.

You print a shirt, it looks great—a beautifully-printed cute frog on a nice, soft garment dyed light green shirt. You quite happily send it on its way. You got the order last minute, cranked it out and boxed it so fast that they might even open them on the other end still warm. You even allow yourself to dream of the check arriving quickly (really dreaming here) and maybe, just maybe, even a rare compliment might hit your inbox in a couple of days. But when the customer calls, they instead sound like they did graduate work at Cursing College, asking about the faint white frog you printed on the bottom and back of the shirts. 

When you get the shirt back, sure enough, there is a faint pale silhouette of the frog you printed in full color on the backs of most of the shirts and on the tail ends of some others. Are the shirts haunted? No, the shirts are ghosting—all 14 cases of them. Now that is a real horror story. To fix this predicament, who you gonna call? Unfortunately, The Ghostbusters can’t even help with this one.

Paranormal analysis

Ironically, ghosting is often the result of efforts to prevent other scary things from happening to shirts. It can happen when printing low-bleed white ink on a colored shirt. The color of garment-dyed shirts sometimes comes through the white ink printed on them. It is tempting to use low-bleed ink to stop this but, in fact, ghosting almost only occurs with low-bleed ink. And, in fact, low-bleed white ink will almost never stop the dye migration or “bleeding” that happens with garment-dyed shirts. 

Ghosting happens when low-bleed white ink reacts with certain dyes in certain shirts. It only happens in certain conditions, making this all the more maddening. It mostly happens on light blues, violet, yellows and greens and not on as much on dark colors like navy or black.

Some of the chemistry in some low-bleed inks integrates some oxidation/reduction reaction with certain dyes present, particularly in 50/50 fabric—great if you are trying to kill the color coming out of the fabric. However, this same oxidation/reduction action on certain 100 percent cotton shirts spells disaster. This reaction occurs most strongly in the presence of heat and humidity. This reaction also keeps going when the ink has not cured. It is most likely to happen with certain types of dyes and certain colors, as previously mentioned.

Haunting grounds

Here are a few elements that create a likely scenario for ghosts to haunt garments:

1) A large patch of white low-bleed ink—i.e. the big frog and its white under print (pictured).

2) A light green 100 percent cotton shirt—possible blue and yellow dyestuffs making green.

3) A humid day—it’s more likely that the moisture does not fully evaporate from the shirt in the dryer. As the extra water comes out of the shirts, the ink won’t cure as well. Evaporating water cools the shirt.

4) Using a dryer with a short heat chamber—less time for moisture to evaporate, less time for the ink to fully cure and the higher temp (you either need more heat or longer time) has the shirts coming out at a higher temperature.

5) Using a dryer with a short take off—the shirts are burning hot coming off the dryer.

6) Going at a fast printing pace—faster through the dryer means it’s less likely they’re fully cured, are hotter in the piles of folded shirts and, if in a rush, means that the shirts are boxed while still very hot.

The bottom line is that low-bleed ink will continue to do its thing because it isn’t cured. It stays hot because you are stacking up the shirts on top of one another and thereby insulating them. This stacking keeps the heat and moisture in, and the low-bleed chemistry reacts with those dyes it likes, turning them white. 

Prevention: give up the ghost

As with so many problems in screen printing, they are either solved or made better by good basic printing. The right mesh, a good and level press, good squeegees, the proper off-contact and good screen tension for appropriate ink lay-down should be in place.

• Use low-bleed ink only when necessary—use cotton whites for 100 percent cotton and low-bleed only for 50/50 blends. Several ink companies make a low-bleed non-ghosting white ink for jobs that will run both cotton and 50/50 shirts.

• Lower the moisture content of the shirts by putting them out on carts before printing. If shirts came from a damp truck or warehouse, they can have lots of moisture in them. Consider running air conditioning in the shop during very humid months. 

• Be careful when using an unknown shirt supplier, particularly with yellow, light blue and light green colored shirts. Also watch out when printing garment-dyed shirts.

• Cure the ink properly. Don’t over flash or over heat the shirts in the dryer.

• Try and keep the shirts cooler by a longer out-feed to your dryer—setup a fan to blow on the shirts or, in desperate circumstances, stack the shirts in a bunch of piles rather than one shirt on top of the next.

• Check if the ink/fabric combo is susceptible to ghosting by using a test for ghosting (see sidebar).

• As always, work with reliable suppliers of inks and of shirts. The result is fewer problems and, when a problem does arise, more solutions and honest answers. 

Just one more scary outcome to fear in our profession, yet with the right black magic (a.k.a. some good, common basic printing technique and a little caution), you can give up the ghost.

Ghost Test

1) Print white ink on the fabric of the shirts that will comprise the order. 

2) Place that test fabric in a transfer machine and spray it with a mist of water.

3) Place a piece of the unprinted shirt fabric on top.

4) Apply medium pressure with the heat press set on 250°F for a half hour.

5) Check for ghosting on the unprinted fabric