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News Release from: MacDermid Autotype | Subject: Screen printing moiré effects
Edited by the Printingtalk Editorial
Team on 18 February 2005
Explaining Moiré Effects In Screen
Printing
Professor Stephen Abbott of Autotype International, here presents the first part of a four part series looking at the subject of moiré effects.
Professor Stephen Abbott of Autotype International, here presents the first part of a four part series looking at the subject of moiré effects Screen printing without the inconvenience of moiré effects would make life much easier for all screen printers
This article was originally published on Printingtalk on 18 Feb 2003 at 8.00am (UK)
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The bad news is that it is almost impossible to eliminate the impact of moiré entirely.
The good news is that the effect can be controlled and reduced to a level where it is no longer a problem.
In forthcoming articles we will discuss cures for specific types of moiré effects and provide some proven recipes for success but first we must understand exactly what moiré is and how it occurs.
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Not many people know that the word moiré comes from Angora goats as explained by the 1911 Encyclopaedia: 'MOHAIR - the hair of a variety of goat originally inhabiting the regions of Asiatic Turkey of which Angora is the centre, whence the animal is known as the Angora goat.
The Arabic mukhayyer or muhayyar from which the word came into English, probably through the Italian Moccacaro or French Inocayart, meant literally, 'choice' or 'select' and was applied to cloth made from goats' hair.
In the 17th Century the word, which before appears in such forms as mocayare or mokaire, became corrupted to the English 'mohair' from which the French adapted moiré, a 'watered silk fabric.' Moiré has since become the term used to explain the effect with which we are all familiar - we see shimmering clothes on TV presenters and ugly patterns in our screen prints.
A moiré pattern is produced by superimposing a repetitive design, such as a grid, onto a slightly displaced design, either of the same or different nature, in order to produce a pattern distinct from its components.
The human eye has evolved to be sensitive to patterns.
For example, to the eye, as you pass under a bridge the railings at the front of a bridge are spaced slightly differently to those at the back.
If the moiré comes from the railings of a bridge, as you drive underneath it you can see a moving moiré pattern as the front and rear railings shift in their relative positions.
The moiré pattern stays the same but the dark and light areas move along in sequence.
To create a moiré effect you need regular patterns that differ in some way.
In the above example the difference was caused by the apparent spacing of the railings.
Sometimes though, the difference is caused by overlaying patterns at different angles.
The basic cause of our moiré problems remains the same: regular but different patterns overlaid over each other, combined with the way in which the human eye interprets the picture.
Now that we have an understanding of the fundamental cause of moiré effects, in the next part of this study, we can go on to consider their more subtle incarnations and how they can be cured using proven recipes for success. Request a free brochure from MacDermid Autotype ...
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