SMR Premium Vellum Tips & Tricks

Many printers wonder: "Could I really use vellum and cut my photographic costs?" Most printers who don't believe they can use vellum have tried, and failed only because nobody had shown them how to properly use vellum. It is true that not every screen printing job can successfully use vellum to replace film positives. Extremely fine alignment jobs, such as 4-color process, and very large sized jobs with tight alignment needs often disqualify themselves as candidates for using vellum. However, for most screen printing jobs in the textile and small signage fields, vellum is usually a better answer than film positives.

Most reasons why printers believe they cannot use vellum fall into two categories. Either they think that they cannot get a dense (black) enough image from their computer printer, or they contend that due to shrinkage under the heat of a laser printer's fuser, the vellum shrinks and an adequate alignment becomes impossible. Both of these objections are easily overcome through the use of proper techniques.

Inadequate Density - Laser Printer: Many laser printers do not produce a dense enough image on any carrier to expose a screen properly. There are a number of ways to get a better image without getting a new laser printer:

• Keep your laser printer in top shape. If possible, do not use refurbished toner cartridges, as they do not provide as dense an image as is provided by a factory - fresh cartridge.
• Experiment with your printer to find the darkest toner setting you can get without toning. Toning is the word used to describe the gray shading in blank areas when too much ink or toner is used by a printing device.
• Even a weak printed image on vellum can be improved dramatically. After printing on vellum, lightly spray Krylon tm Artist's Matte finish spray #1311 on the image side of the paper. This spray is usually available at most hardware stores, and at almost any art store. A light spray of this substance can make a relatively transparent image appear dense and black. (You really have to try this to believe it! It works great!)

Inadequate Density - Ink-Jet Printer: Most ink-jet printers can produce a vellum image dark enough to burn a screen, but few printers know how to adjust the printer setup dialog to attain an adequate amount of ink laydown.

• In the printer setup dialog, most ink-jet printers ask you to select a type of paper that is being used. Set the paper type to a very absorbent paper, such as plain paper or card stock. If your printer has a vellum setting, this is probably not a good choice for your purposes! Even though vellum is not very absorbent due to it's extreme density, you will want to select the most absorbent paper type possible where the ink will not run from the sheet.
• Use regular ink! Many printers have purchased specialty ink-jet inks for use on film or other substrates. While these inks work great for their intended purpose, they usually cause problems printing on vellum. Regular ink-jet ink that you buy off the shelf for your printer usually works best.
• Use your multi-color ink cartridge if possible - or when needed. Some (but not many) ink-jet printers have a dialog in the printer setup that allows you to select to use all four colors (Cyan, Magenta, Yellow, and Black) when printing black items on the page. This gives you nearly 4 times the density of ink if you need it. Most cheaper ink-jet printers come with just a multi-color cartridge, and you have to purchase a black cartridge separately as an option. If you don't insert the black cartridge on these models, the printer will create all black areas by applying all 3 colors, again dramatically increasing the density of your print.
• Allow adequate time to dry. Vellum is less absorbent than regular paper, and it takes longer to dry - roughly one minute per sheet to be "dry to the touch." Make sure that vellum positives are allowed to dry in a horizontal position (laying down) and that subsequent sheets emerging from the printer are not allowed to land on top of previously printed sheets.

Tip: Most modern screen printing emulsions do not require nearly as dark of an image as many printers believe they need. Please make certain you know how to determine a correct exposure before determining whether an image is dense enough. Click Here.

Laser Toner Flakes Off: While vellum is translucent and might seem to be "Lightweight," vellum is actually one of the most dense substrates you can run through your printer. Toner flaking - which might be observed as dark powder rubbing off from separations, chips in the image, or toner sticking to areas of screens after exposure - is a result of inadequate fusing. Modern laser printers have driver software designed to apply the minimum amount of heat required to prints you make, in an effort to extend the longevity of the heater (fuser) unit, and safeguard delicate papers. The biggest mistake most printers make is in failing to select the paper type when printing vellum, or - worse yet - setting the paper type to a substrate that cannot accept much heat, such as "Transparency." (The "transparency" setting is one of the lowest heat settings on your printer)

When printing on SMR Premium vellum you are printing to a substrate that has as much heat-absorption capability and heat-requirement needs as heavy, coated cardstock. You would have a very hard time scorching SMR Premium vellum in your laser printer. For most jobs - and especially when using large sizes of vellum stock - you will want to choose the hottest setting your laser printer can deliver. Heat settings are determined when you set-up your printer by choosing paper types. Look for the thickest, most heat-requiring paper in your printer's setup dialog. Look for choices such as "Thick," "Cardstock," or "Rough."

Some older printers do not have paper-type selections. These printers usually run the fuser (heater) at it's highest setting at all times, and usually do a great job on Vellum. However, as printers age, the fuser unit becomes weak, eventually failing. At some point, the fuser becomes too old and weak to properly fuse the toner on vellum.

Poor Alignment - Laser Printers: Laser printers use heat to fuse toner powder to the paper carrier. Alignment problems with vellum are caused by paper shrinkage when the laser printer's fuser heats the paper, and humidity in the stock escapes and / or certain elements of the paper itself react to the heat. If the vellum you are using is all cut with the same "grain," then the paper should all shrink relatively proportionately. This means that even though a slight shrinkage has occurred, it has occurred in the same dimensions on each sheet of the separations, so the sheets should still line up.

Still other problems are caused by the laser printer's inadequacies as well. Your laser printer uses measurements based on various points of reference to place each dot of toner on the sheet. The fact is, even if your paper were perfectly dimensionally stable, your laser printer would still make some small mistakes in alignment due to which reference points it used to plot one line vs. another. For most screen printed art, using most good-quality laser printers however, this error is negligible. To make alignment problems as minimal as possible:

• Make certain all papers in a separation set have the same grain. Never use vellum from two different packages in the same separation. Also, never "gang" two separations on the same page, facing different directions.
• For critical separations, pre-shrink the vellum before printing on it. The best way to pre-shrink the vellum is to run it through the laser printer before you print on it. Do this by printing a blank page onto the vellum with your art program, such as by printing an entirely white object. Make certain you run it twice, once on each side.

Poor Alignment - Ink-jet Printers: When you consider that an ink-jet image is created by a paint head running back and forth on a bar, it is a miracle that ink-jet printers can produce pages that line up at all. Yet, most ink-jet printers line up fairly well. Some printers do not reproduce exact sizes well, however, in which case no type of paper or film will be of any help. SMR Premium vellum is relatively moisture resistant, and does not usually shrink in the ink jet printing process. Extremely large areas of solid ink laydown can, however, cause moisture distortion, and jobs with such areas that require tight registration might not be suitable for vellum use.

Tip: Before you expose screens in a multi-color job from the vellum positives you have printed, place the positives on a light table and look to see how well they line up. If you placed centering marks in all four corners, most printers find that - if their computer printer is capable of holding good registration - less than 1/100 of an inch of variance should have occurred between separations. That is usually good enough for all but the tightest registration on jobs. If you burn screens from positives that lined up well on the light table, but they don't line up well at the press, then your problem is not in the vellum! Most printers who complain that jobs don't line up (whether they used vellum or other methods of creating separations) fail to get good registration due to factors in the screens themselves, or failure to level screens to the platens and properly use off-contact.

Paper Curling: Being a type of paper, sometimes vellum (and transfer release paper) curls up on the shelf. This happens when the paper is allowed to absorb humidity from the air around it. While SMR premium vellum is more resistant to humidity problems than many other brands, small problems can be noticed, especially if pre-shrinking is performed. To avoid curling problems:

• Store vellum in an area of low humidity. One strange, yet very well-working solution is to store vellum - well sealed - in the refrigerator.
• When pre-shrinking vellum in your laser printer, make sure you pre-shrink once on each side so the moisture in the paper is treated evenly.