Putting a glow in your presswork - OBAs and black light posters

Most printers who are faced with a printing job that's intended to glow under black light tend to think only about the issues of printing with fluorescent inks (see the post HERE). However, there is another important item that needs to be considered and that is the effect that the amount of, or lack, of OBAs (Optical Brightening Agents) in the paper will have on the final result.

For example, viewed under a black light this poster "glows" in an expected way:And it will look similar, except for the glow effect, under normal room and black light conditions.

However this poster which has large areas of white, i.e. unprinted paper, looks very different under normal house light:compared with being viewed under black light:
The difference in appearance is caused by the amount of OBAs in the paper. In this example, the paper contains low/no OBAs. Under normal home lighting the paper looks white and the fluorescent inks fairly bright. However, under black light the inks glow brightly but the paper which contains low/no levels of fluorescing agents goes dark - there is effectively no light for the paper to reflect.

This difference in color response can be used creatively or it could destroy the intended look of the poster as envisioned by the artist.
If a paper with high levels of OBAs is used instead, then the appearance of the image would be preserved under black light:
So, when quoting a "black light" job consider the amount of OBAs that the paper contains because it can have a profound effect on the final result. If the paper will have 100% ink coverage then choose a paper with high OBA content to assist in the final glow effect. If the design includes areas of white, then discuss the issue with the original designer and choose a paper that has high, or no OBA, content according to the final result the designer is trying to achieve.

To determine the relative amount of OBAs in the paper, view a sample using an inexpensive fluorescent type black light:

Choosing the right screen angle for over-printing spot colors

To decide which screen angle to use when a screened PMS/spot color overprints a 4/C process image you will need to look carefully at the image that you will be overprinting.

The basic rule is to use the screen angle of the least prominent (or missing) screened process color that will be underneath the screened spot color.

For example, if there's no screened black under the spot color - use the Black angle, if there's no Cyan use the Cyan angle, etc.

Try to avoid using the Yellow screen angle because in standard screen angle sets yellow is only 15 degrees away from C or M. As a result moiré is always there but it is usually not visible because the yellow is so pale. The moiré can become visible however, if the yellow becomes contaminated - or if it is used for a dark spot color.

For example, in the graphic below, the left image is Cyan (at 105°) overprinted with process Yellow at the standard 90°. The moiré is barely visible. However, in the center image overprinting Cyan with PMS 144 – a very dark yellow/orange color – using the same Yellow screen angle results in the existing moiré becoming very visible. On the right, PMS 144 uses the Magenta screen angle (75°) instead which eliminates the halftone moiré seen in the center image.

Alternatively, you could try running the 5th color using a second order FM screen. If you're using a 175 lpi AM/XM screen then the FM should be about 35 micron because if it's any finer you'll need to create dot gain compensation curves for the FM. Because 35 micron is a fairly coarse screen it is best used for fairly light colors otherwise you may find that the screen is too visible.

Because spot/PMS colors are typically formulated to be printed solid and not halftone screened, make sure that your ink vendor knows that you are going to be screening the ink and the dot size range as well (either in microns or lpi) so that they can formulate the inks accordingly.

Hi-Fi color - 8 strategies to implementation

There are basically 8 established ways to print contone images with added vibrancy – i.e. Hi-Fi color. Most require a great deal of testing and experimentation. Many will be problematic from a proofing point of view, however, the testing process can often provide samples that can be used give buyers a good enough idea as to what their specific finished product would look like. Note that the extra vibrancy achieved on press with these processes is dependent on the gamut of the images selected for this process. Images that are already well housed within the standard cmyk color gamut will likely not benefit from the Hi-Fi gamut and therefore show no visible difference compared to a standard four color process image.

In order from simplest to most complex:

1) Increase solid ink density.
Solid graphic is 175 lpi gamut at standard SIDs. Translucent graphic is 175 lpi gamut at higher SIDs.
Solid ink densities can often be increased by about 20-30 points from industry standards on presses which have aqueous coaters. Curves are applied to plate to normalize dot gain (restore tone reproduction). Extra saturation affects all color areas on the page. Testing determines the max density that can be achieved before presswork color becomes unstable, or ink slinging or tailing occurs. Uses existing CMYK images. This is the simplest approach to add punch since the only thing in production that needs to happen, once testing is complete, is to have a curve applied to the plates and new SID targets communicated to the pressroom for jobs targeted for the extra vibrancy. A popular strategy because it does not require anything to change other than a curve applied to the plates. It will increase overall color saturation but may not increase the gamut in areas where CMYK is weak (oranges and purples). A more complete explanation of the process begins HERE. A variation on this method would be to run CMYK at normal SIDs and then do a second hit of CMY also at normal SIDs.

2) Use FM screening.
Solid graphic is 175 lpi gamut using standard inks. Translucent graphic is 20 micron FM screening gamut.
Going to a finer screen, either 20 micron FM or greater than 385 lpi AM/XM screening will provide about 10-15% greater gamut volume compared with 175 lpi AM/XM screening. The extra gamut will be available in one and two color screen tint builds only.


3) Big Gamut CMYK
Solid graphic is 175 lpi gamut using standard inks. Translucent graphic is 175 lpi gamut using wider gamut CMYK inks - Toyo Kaleido inks in this example.
This method uses higher pigment load inks, or spectrally purer colorants (and therefore more expensive inks). Examples are Toyo Kaleido inks and (BASF) Flint Novaspace f 2010 inks. Extra saturation affects all color areas on the page. This method uses existing CMYK images, however existing separations may produce unexpected results. From a production point of view, washups and ink change overs will happen when switching from regular CMYK to Big Gamut CMYK jobs.

4) CMYK plus "bump" (touch plate) color.
Solid graphic is 175 lpi gamut at standard SIDs. Translucent graphic is extra gamut resulting from the addition of a special Orange and special Blue.
Adds gamut only where needed (e.g. oranges, blues, etc.). Manual process in Photoshop to create 5th plate. Requires testing and experimenting to establish workflow. Uses existing CMYK images with added spot color channel to add extra vibrancy within specific images only. Note that the extra ink(s) will need to be formulated to wet trap, be screened, and have a dot gain similar to its closest process color. E.g. Red ink would mimic Magenta in lithographic performance. This method is usually used in fine art reproduction, catalogue, and automotive work to bring specific colors into gamut.

5) Swing process colors.
Solid graphic is 175 lpi gamut at standard SIDs. Translucent graphic is extra gamut in the blue range resulting from the substitution of a violet for the standard process Cyan.
This uses a standard CMYK ink set where one of the process colors, usually magenta but sometimes the cyan, is swapped out for an alternate. For example, the standard process magenta might be swapped out for a PMS Red 032, Warm Red, Rhodamine Red, or even PMS 2395. This distorts the entire gamut but can be very effective depending on image content. For example, a photo of an orange against green leaves would really pop if a warm red is used instead of a conventional magenta. This method is best used where there are no skin tones present since skin tones would look quite odd. Note that all image content is affected, including text. Requires a lot of experimentation and documented samples.

6) Big "H" Pantone Hexachrome.
Solid graphic is 175 lpi gamut at standard SIDs. Translucent graphic is extra gamut resulting from the use of proprietary Pantone Cyan, Magenta, Yellow, Orange and Green.
Uses a proprietary 6 color inkset with fluorescing agents in their pigments. Extra vibrancy affects all color areas on the page (images and text). Inks tend to have poor printability. Expensive. Manual process to do separations in Photoshop. It often delivers images that have an "artificial" look. Colors can appear garish rather than natural. Requires testing and experimenting to establish workflow. Complex separated workflow (DCS 2 files).

7) Small "H" Hexachrome.
Solid graphic is 175 lpi gamut at standard SIDs. Translucent graphic is extra gamut resulting from the use of Orange and Green.
Uses standard CMYK inks plus Orange and Green inks to expand Gamut. Uses Pantone Heximage software from Pantone to do manual separations to 6 color process in Photoshop. Extra vibrancy applies to images only. This method is popular in the label and packaging markets. It can be a good compromise compared to process 5. Complex separated workflow (DCS 2 files).

8) CMYK plus "extended" process colors.
Solid graphic is 175 lpi gamut at standard SIDs. Translucent graphic is extra gamut resulting from the use of Red, Violet, and Green "extended" process colors.
ICC profile based workflow. RGB in and separated to CMYKRG or CMYKRV, or CMYKRGB out. Fully automated process. Requires profiling the press using the appropriate inkset. Creating an RGB to CMYKXX separation profile. The profile is used by the workflow to separate the images as part of the process plan, as delivered to the workflow as a preseparated file. Extra vibrancy applies to images only.