The purpose of film is to block UV light during screen exposure. Films may or may not look dark, but the UV light blocking ability is what is key and not necessarily how the ink appears on the film. How can you tell if they have the right dMax (density)?
Most users will NOT have the proper transmissive Densitometer to read the actual percentage of light that is being blocked by their films. You rely on your “eyes” and that is NOT the best way.
First, understand that “density” is not the “only thing” that matters, it’s the amount of UV (Ultra Violet Light) that is blocked that really matters. Just as with the older product called Rubylith that we cut with x-acto knives to make films, you can see through it, but it blocks 100% UV light making it perfect for screen making.
Density vs UV blocking:
Light can be blocked through density alone since light can not pass through a solid object, but films are not 100% solid. Pigment inks because of their properties can read a higher Density value (appear blacker) than Dye ink, but test a dye ink for its UV blocking and you will be very surprised. A dye film that only reads 2.63 Density can have a UV reading of more than 5!
Our dye inks (All Black Ink™ )(Dmax™) and some others have a UV inhibitor mixed in so even if you can see slightly through the films you will notice a red tint. This is the UV blocking agent that makes it all work well.
Human eye test for those that do not have a Densitometer:
Dye ink – if you hold your film up to a bright light or a bright window you should see slightly through the 100% print areas so that images look very dark and lacking detail and the overall appearance should have a red tint about it. That is probably close to a 3.0 dmax with light UV blocking and that is good. If your films looks like a pair of tinted sunglasses then obviously that is too light. Adjust your RIP settings and try again.
Pigment ink – is obviously different, it’s not a water based ink like dye, its archival inks for sign making and has a chemical base with radical particles that form a light blocking bond, so when using pigment ink and using your “eye” to evaluate the result you are looking for a solid or as close to a solid black film as possible.
Use AccuRIP’s Droplet Weight Density TEST Print feature under AccuRIP’s File Menu (not available in SE). It will produce 15 droplet weights per resolution. Print the test to film. Let it dry, then expose a screen. Wash it out and review the result,
Cost? Pigment inks and film cost more which is why so many users choose dye.
Availablity: Dye is easier to get through industry suppliers.
The use of waterproof film is critical to your success. Nott hat non-waterproof will not perform in some cases – it is not recommended. The emulsion layer on the film grabs the ink.