One of the easiest ways to avoid moiré is to use the flamenco method of single angle spot (half tone alignment) when printing out films. What is the flamenco method?
Printing using the flamenco method accepts up to 40 percent press gain without the loss of detail or the corruption of color due to dot gain. The reason is that there is a lot more room between each spot (half tone) allowing for the physical gain of the ink that eventually increases tonality and color. With a rosette pattern the space between each spot is greatly reduced due to the angle shifting. Since screen print presses are high saturation devices that top out around 33 percent, flamenco method printing never over gains, allowing for very deep clean runs with little to no down time.
Rosette printing has trouble with as little as 15 percent dot gain. Print your spot process and all other separations (even cmyk) using single angles to improve your prints. It’s even advised that you print your color prints for a color laser printer using flamenco. A simple test with a cmyk file at 55 lines per screen (correct wording?), one as flamenco and the other as standard rosette angles will prove it all.
This becomes even easier when using AccuRIP™, as it already prints in the Flamenco method by default.
If you are printing half tones with a rosette pattern, one thing you can count on is moiré. No matter how careful you are the dreaded patterns will appear in your prints. Months may pass without moiré problems, but then you will get hit with a slew of images in which moiré seems uncontrollable. You can take steps to greatly reduce the occurrence of moiré in your prints.
Tips To Help Avoid Half Tone Moiré:
1. Always Be Consistent, Systematic and Organized.
2. Work From a Constant Set Of Values
3. Never Assume What You Have Is Correct
4. A Half Tone Line Count and Mesh Count That Give the Highest Mesh to Dot Ratio
5. Choose The Mesh With The Highest Percent Open Area and Thinnest Thread Possible
6. When Using Direct Emulsion, Maintain Eight-12 Microns Over Mesh
7. Use Pre Registration Board To Align Positives To Screens
8. Maintain Full Positive To Screen Contact With Correct Exposure