Using Vellum to Burn Screens by Scott Fresener

By Scott Fresener For those who remember the old process cameras, when vellum paper and laser printers found a home in the screen making department back in the early 90′s we thought we had found nirvana. We went from a darkroom to pressing the Print button and from film costs of over $2.00 per film to less than $.25. What more could we ask for? For every day general work vellum was and in some circles still is the workhorse of screen imaging. In the early 2000′s guys like me were looking for a better way to make screens for more critical jobs. The birth of inkjet printers, software rips, special clear film and ink, spawned the birth of making film positives that rivaled camera quality. But, for much of the “ink slapping” work being done it was still almost too good.  The films could cost $1.00 to $1.50 compared to….. vellum at $.25 to $.50. Over the years I sold thousands of inkjet printers and FastRIP packages and one thing I found interesting was that a LOT of my customers kept their laser printer and still used vellum for those non-critical jobs. I can’t blame them.

Why Vellum?

It’s a pretty simple answer – cost. Vellum paper can be printed on a laser printer or copier and costs 10 to 50 cents (depending on size). With this kind of saving it doesn’t take long to figure out what makes vellum so attractive.

Is Vellum for Everyone?

This depends on who you talk to. Some printers have tried vellum and hated it. Others just use vellum for certain jobs. It really depends on the type of work you do. I truly believe there is a silent majority of printers who only do one and two color prints and NEVER do tight register multi-color work or process color. Our industry does a disservice by not qualifying hard statements like “it won’t work.” Won’t work for what? Process color? Perfect register? One color print? Twelve shirts? No, vellum is not for everyone. But there are millions of shirts printed that would never be “award winning” yet go to very happy customers.

The Problems With Vellum

Shrinkage

The major problem with vellum is that it isn’t as stable as polyester based film. Being a paper, it can absorb moisture in the air and change shape when heated with the fusing rollers in a laser printer. This means that vellum isn’t good for really tight register jobs. If printing a butt register job you will find it almost impossible to get the vellums to line up in perfect register.

Difference in Brands

Another problem is there are different brands of vellum and laser printers and some are better than others. Although the term “vellum” is a paper industry term for a smooth finish, the best vellums for screening have a slightly “toothy” finish. This allows them to accept more toner from a laser printer. It also keeps them from jamming in a laser printer. Some laser printers are not designed to work with really smooth finished paper. Unfortunately, some laser printers and copiers do not lay down a thick enough deposit of toner – regardless of the vellum paper you use.

Not Good With Halftones

Since the toner deposit is not as dense as on a film, vellum will not work well for detailed halftone dots because the exposure light will just burn through the weak toner. This means that if you use vellum on a process color job you will probably lose the 5% and 10% dots. Not Good With Tiles and Halftones Although you can tile together pieces of a design, you should NOT tape vellums together where there are halftone dots. You will never get the dots to match up perfectly and the extra layer of paper will block too much light.

Where to Get Vellum

The best source is through the screen printing industry. Many screen print suppliers still carry vellum.  Most of them will send you a sample pack for free. Industry suppliers offer vellum in 8-1/2″ x 11″, 8-1/2″ x 14″, 11″ x 17″, 12″ x 18″ and 18″ x 24″.

How To Overcome Problems

Shrinkage

This is fairly easy. The easiest way to prevent shrinkage is to shrink the paper BEFORE you print the paper out. This means simply printing out some of the paper as blanks through the laser printer to pre-shrink, or simply try running the vellum through the dryer first. Then, put the shrunk paper back in the paper tray and print the job. Such a simple solution for such a hard problem!

Weak Toner Deposit

This is also easy. You can run the printed vellum through your conveyor dryer (or put it under the flash unit) and the heat will remelt the toner and make it darker! Pretty amazing stuff, this toner. If the job is tight register, you may lose some registration by running the paper through the dryer.You can also spray the vellum paper with an artist’s fixative like Krylon to make the toner darker. Suppiers carry sprays that make the toner darker but there is nothing like hair spray to do the same thing.  Your call.

Tiling Images That are Too Small

If you are using a small laser, the vellum positives may be too small for your design. The computer program will have to print the image out in “tiles.” These need to be taped together to work. If you tape vellum paper over an image area, you will have an underexposed area. Try to trim away excess vellum that might cover image areas.

Determining the Correct Exposure

Vellum paper can block as much as 35% of the standard light transmittance of film, therefore it will take a longer exposure time. As a starting point, increase the exposure by 25%. You will obviously know if it is under exposed because you will see that the screen is not as dark where the vellum was during washout. Your emulsion will also be a little slimy on the inside – a sign of underexposure. Some suppliers offer a Vellum Exposure Calculator. This is simply a test vellum (their brand of vellum and laser of choice), with gray neutral density filters taped in place. Simply place this on the bottom of a screen and expose for TWICE the estimated time (you should have a fairly good idea of where you need to be). When you develop the screen you can determine the correct exposure time based on the which “target” looks and feels the best.

How Far Can You Go?

OK, so “they” say you can’t use vellum for anything too hard. Yes, film would be a better choice for the process jobs, but for NON-CRITICAL work or a process job where there aren’t any reference colors and the price of film would be too high, then vellum is the right choice. Of course the next best thing is to go up one step and use Laser Acetate rather than vellum for more critical jobs. It is a little more expensive but much more stable. And, if you are real serious about halftones and higher end printing then your next step is an inkjet printer with software rip. Remember, use the best material for the job. For most of the silent majority vellum is the perfect choice.
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