Screen E-Book (.PDF) - MacDermid Autotype

Moire, causes and cures94fluential article from ScreenPrinting 1991.From MacDermid Autotype, Joe Raymondand Bill Appleton and David Parker havebeen exceedingly helpful in all sorts ofways. Finally, Mike Ware of Wasatch Inc. isto be warmly thanked for his insights intomoiré coming from his expertise in thefield of RIPs.Terminology can be tricky in screen printing,so remember to refer to the glossaryto help make it clear what I mean by thevarious terms.The majority of the readers of this eBookwork in lpi and dpi so the examples are definedin those terms. The conversions intometric equivalents (lpc, dpc) are roundedfor convenience.Angora goatsNot a lot of people know that the wordmoiré comes from Angora goats! Here’s anexplanation from the 1911 Encyclopaedia:“MOHAIR, the hair of a variety of goat originallyinhabiting the regions of Asiatic Turkeyof which Angora is the centre, whencethe animal is known as the Angora goat.ريخم The Arabic mukhayyar or muhayyarfrom which the word came into Englishprobably through the Ital. moccacaro or Fr.inocayart, meant literally, ‘choice’ or ‘select’,and was applied to cloth made of goats’hair. In the 17th century the word, whichbefore appears in such forms as mocayareor mokaire, became corrupted to the English“mohair” from which the French adaptedmoiré, a watered silk fabric.”It then became the general word for theeffect we are all familiar with when we seerailings on bridges, shimmering clotheson TV presenters and ugly patterns in ourscreen prints. There was, alas, never a ProfessorMoiré who discovered the maths ofthe effect.Moiré mathsYou don’t need to know any maths to understandthis section. But moiré is a mathematicalphenomenon and can only beanalysed properly using some powerfulmathematical techniques.The results have all been produced frompowerful computer models. The goodnews is that there is an exact match betweenthe outputs of the models and thefacts of real life.One of the models, the Moiré Mesh Calculatoris part of the MacDermid AutotypeDSP which can be downloaded from thiseBooks’ website.