Screen Printing Film Positives: How to Print and Check Them
Screen printing film positives: what they do, inkjet film and opacity, how to print them, outsourcing vs in house and a film problems checklist.
Decorator guide to film positives: why the black must block UV light, choosing waterproof inkjet film, getting dense black from a printer, a step by step print routine, outsourcing vs in house and a f
Screen printing film positives are opaque black images on clear film that block light during screen exposure, so the emulsion under the image stays soft and washes out. Print them on waterproof inkjet film with the densest black your setup can make, check opacity before you expose, and add registration marks so multiple films line up.
The one rule: what matters is how much UV light the black blocks, not how dark it looks to your eye. A film that lets light through gives weak, washed out detail no matter how good the art is.
Part of the screen printing guides in the DAX Learning Hub. New to the process? See Screen Printing for Beginners.
What a Film Positive Does
During exposure, light hardens the emulsion wherever it reaches it. The black areas of the film shield the emulsion under the design, so those areas stay soft and rinse out to become the open stencil. If the black is not dense enough, light leaks through, partly hardens the emulsion under the image, and fine detail fails to wash out cleanly.
Clear areas matter too: smudges, dust and fingerprints on the film can block light where you want it and show up as defects in the stencil. Handle films by the edges and keep them clean. Exposure itself, including how to find the right time, is covered in Emulsion Exposure Times.
Inkjet Film, Printer and Opacity
Film
Use waterproof inkjet film made for screen printing. It has a coated side that grabs and holds the ink; printing on the slick side makes ink bead and smear. Generic transparency film often cannot hold enough ink to block light reliably.
Printer and ink setup
A standard inkjet driver usually does not lay down enough black on its own. Shops get dense film by printing black only where the driver allows, by converting a printer to an all black ink setup, or by using RIP software built for film output. Keep the print head maintained: clogged nozzles show up as banding on the film and then in the print.
Checking opacity
The quick check is to hold the film against a bright lamp or window. If you can clearly see light through the solid black, UV light will pass too. Because eyes cannot see UV, a transmission densitometer gives the real answer. Published guidance generally puts usable film density at roughly 3.5 to 4 or higher on that scale; check your film and ink supplier's spec.
| Check | Pass | Fail |
|---|---|---|
| Bright light test on solid black | Little or no light through the black | Lamp clearly visible |
| Edges of text and fine lines | Sharp, solid edges | Fuzzy, beaded or broken |
| Clear areas | Clean, no smudges or ink spots | Fingerprints, dust or stray ink |
| Densitometer (if you have one) | Meets the supplier's density spec | Below spec |
How to Print a Film Positive Step by Step
Settings vary by printer and film, so treat this as the routine and your supplier's instructions as the spec:
- Finish the separation for one color per film, in solid black, using your artwork file prep checklist.
- Add registration marks outside the design on every film for that job, in the same place on each.
- Load waterproof film with the coated side facing the print head.
- Set the driver or RIP for the densest black output your setup supports.
- Print, then check the film against a bright light and inspect fine lines and text.
- Store finished films flat and clean in a folder labeled with the job and color.
For halftone art, line count and dot settings belong in Halftone Screen Printing.
Registering multiple films
For multi color jobs, put registration marks on every film and line the films up on the screen with a center line and a T square or a fixed template, so each color lands in the same place from screen to screen. That consistency saves time on press.
Outsourcing Film vs Printing In House
Many shops start by outsourcing films and bring them in house once volume grows. In house printing costs film, ink and printer upkeep, and print heads need regular use and maintenance to stay reliable.
| Factor | Outsourcing film | Printing in house |
|---|---|---|
| Startup cost | None beyond per film charges | Printer, film, ink and possibly RIP software |
| Turnaround | Depends on the service and shipping | Same day, on demand |
| Density and quality | Set by the service's equipment | Depends on your setup and maintenance |
| Upkeep | None | Head cleaning, nozzle checks, regular use |
| Fits | Low volume or occasional jobs | Steady jobs and quick changes |
Film Problems Checklist
| Problem | Likely cause | What to check |
|---|---|---|
| Light shows through the black | Not enough ink, wrong film side, standard driver settings | Coated side, black only or RIP output, density |
| Ink beading or smearing | Printing on the slick side, too much ink for the film | Film orientation, media setting |
| Banding lines in solids | Clogged or misaligned print head | Nozzle check and head maintenance |
| Fine detail not washing out | Film density too low | Opacity, then exposure test |
| Colors not lining up | Missing or inconsistent registration marks | Marks on every film, same position |
Frequently Asked Questions About Screen Printing Film Positives (FAQ)
What is a film positive?
A black image on clear film that blocks light during exposure so the design area of the emulsion stays soft and washes out into a stencil.
Can you print film positives on any printer?
Many inkjet printers can, but a standard setup often does not make dense enough black. Shops use black only output, an all black ink conversion or film RIP software.
How dark does a film positive need to be?
Dark enough to block UV light. If light clearly shows through the black against a lamp, it is not dense enough; a densitometer gives the measured answer against the supplier's spec.
Should I outsource film positives?
Outsourcing suits low or occasional volume. In house printing pays off when you need films often and fast and can keep a printer maintained.
Why won't my image wash out of the screen?
Light may be leaking through a thin film and hardening the emulsion under the design. Check film density first, then run an exposure test.
Figures and methods here are hedged starting points that vary by product; confirm every setting against the supplier or manufacturer spec sheet. Film, ink and printer settings vary; follow the film and ink supplier's instructions and spec.
Browse more guides in the DAX Learning Hub, and check cities and dates on the DAX show schedule when you are ready to see film output, exposure and screen room suppliers with suppliers in person.