Inkjet film positives usually come out too light because a standard printer driver lays down a thin layer of ink meant for paper, so UV light leaks through during exposure and the screen washes out soft. The fix is in the output chain, not the artwork: waterproof inkjet film, a RIP or a dense-black driver setting, and often a dye-based black ink set. Underbase, a Windows app from Automata Labs, makes the plates themselves: it writes clean 1-bit film TIFFs and a true-size film PDF, so once your printer is set up for dense black, every plate it prints is solid where it should be.
Separate, choke and output true-size film from the art customers send.
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What does “dark enough” actually mean?
It means the black areas block UV light, not that they look black to you. The help desk for AccuRIP, a film RIP, explains in its article on ink and film density that “The purpose of a printed film positive is to block UV light during screen exposure,” and that films “may or may not look dark, the UV light blocking ability is the key to success.” It compares this to Rubylith, which you can see through but which blocks UV.
The usual measure is film density, often called Dmax, read with a transmission densitometer. Most small shops do not own one, and the same article notes that relying on your eyes is not the best way, since people cannot see UV.
Why does a desktop inkjet print thin film?
ScreenPrinting.com’s guide to AccuRIP Emerald puts the cause simply: “Standard printer drivers print color documents on paper, depositing thin ink layers that allow light to bleed through.” The same guide describes what a RIP adds: control of ink droplet size and support for all-black ink systems, so the printer outputs solid black instead of washed-out grey.
Common causes and fixes:
| Cause | What you notice | Fix |
|---|---|---|
| Standard driver, paper settings | Film looks grey against a window | Use a RIP, or the darkest, highest-quality mode your driver offers |
| Colour inks mixing a “black” | Brownish or purple tint, banding | Print black-only through a RIP or a black ink system |
| Non-waterproof film | Ink beads, smears or stays wet | Use waterproof inkjet film |
| Printing on the wrong side | Ink sits on top and smudges | Print on the coated side |
| Pigment ink | Looks dark but passes UV | Expect to adjust exposure, or consider dye ink |
| Low ink or clogged nozzles | Fine lines or stripes in solids | Run a nozzle check and clean before film jobs |
On ink type, the AccuRIP help desk says it is “very easy to see through pigment ink” and recommends dye, adding that pigment can work but “will require tweaks to your screen exposing supplies and standards.” On film, it calls waterproof film “critical to your success.”
How can I test film without a densitometer?
Two practical tests:
- The window test. The AccuRIP help desk describes holding dye-ink film up to a bright light: you should see slightly through the solid areas, with images very dark and a reddish tint. That is a rough guide for dye ink only.
- The exposure test. Print a strip with solids, fine lines and a halftone ramp, expose a screen with your normal exposure, and wash it out. If solids wash out clean and fine detail holds, the film is doing its job. If the image area is slow to wash out or detail is lost, the film is passing UV. Some RIPs, AccuRIP among them, have a built-in density test print for this.
The exposure test is the one that matters, because it tests your film, your emulsion and your exposure unit together.
Preview the output dots before you print, so you know what the film will carry.
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Can the artwork make film look thin?
Yes, though less often than the printer. Things to check in the file:
- Grey instead of black. A plate that is 80 percent black prints as a halftone or a grey tint, not a solid. Film plates should be pure black and white.
- Anti-aliased edges. Soft edges on a plate print as a fringe of fine dots that may not hold.
- Halftones too fine for the printer. Tiny dots lose density first. Our guide to halftone film positives covers ruling and dot size.
- Resampling at print time. If the driver scales the image, edges and dots get softened.
This is where Underbase helps. It writes each plate as a 1-bit CCITT Group 4 TIFF at 600, 720, 1200 or 1440 dpi, so every pixel is either ink or no ink, with no grey for the driver to interpret. Pick the resolution that matches your printer or RIP. The Output dots preview shows the plate as the film will carry it, at the output resolution, before you print. The film PDF is true size with registration marks and plate labels, and can be mirrored for emulsion-down output.
What does Underbase not do?
Underbase does not run your printer’s ink or replace a RIP. Its own listing says it is not for RIP queues and printer drivers, and that how black the plates print is up to your printer. It does include a built-in help page on film density with what to check before you burn a screen, alongside help on choke and trap, mesh to ruling and troubleshooting.
If your film is thin, a perfect separation still burns a soft screen. Fix the printer side first, then let Underbase handle the plates: separations, a choked white underbase for dark shirts, trapping, and gang sheets that save film.
A quick checklist before a film run
- Nozzle check passes on every black channel.
- Waterproof film, coated side up.
- RIP or darkest driver mode, black only.
- Plates are 1-bit, at a resolution your printer or RIP expects.
- Mirror setting matches how you expose.
- A test strip from today’s film burns clean.
For the rest of the pre-press checks, see our film positive checklist.
Frequently asked questions
Can I just print two films and stack them?
Some shops try this to block more UV. Registration has to be perfect, or edges blur. Fixing the printer output is usually the better long-term answer.
Does Underbase print directly to my printer?
It can print to a Windows printer, or write the film PDF and TIFFs for your RIP or printing workflow.
Do I need a RIP to use Underbase?
No. Underbase makes the plates and film files. A RIP is about how your printer lays down ink.
Will Underbase fix grey film from my current printer?
No. If the printer deposits thin ink, the film will be thin whatever made the plates.
Try Underbase
Underbase is a one-time purchase in the Microsoft Store with a free trial. Open a recent dark-shirt job and compare the plates and film with what went to press. More detail is on the Underbase product page.
Make plates and film from customer art on this PC, with nothing uploaded.
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AccuRIP is a trademark of its owner. Underbase is not affiliated with AccuRIP or ScreenPrinting.com.
Last updated 22 October 2026. Published by Automata Labs, a software company in Canada.