Looking at the perfect angle
Below is a basic representation of how angle affects moiré (and this is only one cause).
I have placed a mesh grid in white over the top of the gradients at different angles on the top two gradients only. The first (0°) represents the screen mesh being stretch perfectly square to the screen frame. Then 22.5°and 45° have the frame rotated at these angles.
To see the effect each angle has on the gradient, you will need to zoom in and out depending on your monitor/ device resolution.
All three angles are now being affected by the thread thickness. While thread thickness on a 120 mesh becomes less of a concern, on meshes such as 43, 62 or 77 thread diameter, does need consideration.
So what did I use?
The print here was a spot colour separation and not CMYK, I used 22.5°on all screens. 22.5° is my go-to angle for all spot colour gradients. However, the angle is created at film output, and not by the screen mesh. This allows me to always stretch screen mesh square to the frame and eliminating waste.
A) 0° should show a slight square grid. B) 22.5° shows little or no moiré. C) 45°will show a slight criss-cross effect.
The different patterns are created by the screen thread hiding parts of the dots, especially the finer dots. The interaction of the screen mesh angle and the angle of the dots created on film (in this case 0°angle on film in all three cases) determine how much of the gradient falls in the mesh holes where ink passes through.
Is there a perfect formula?
Standardising everything you do from outputting films, screen stretching to ink viscosity and squeegee impacts results. The more consistent you are, the better understanding of how each part of the process affects results. The scientific formulas only work if all other elements are consistent and correct. Practice, experiment and enjoy!
The Screen Print Column Thread thickness or diameter
To exaggerate the moiré, I have increased the thread thickness (diameter) of the mesh by 50%. Below you can see how thread thickness alone can have an impact on the level of moiré.
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