Photoengraving - Wikipedia

Photoengraving is a process that uses a light-sensitive photoresist applied to the surface to be engraved to create a mask that shields some areas during a ... Photoengraving FromWikipedia,thefreeencyclopedia Jumptonavigation Jumptosearch Typeofengravingprocess Thisarticleneedsadditionalcitationsforverification.Pleasehelpimprovethisarticlebyaddingcitationstoreliablesources.Unsourcedmaterialmaybechallengedandremoved.Findsources: "Photoengraving" – news ·newspapers ·books ·scholar ·JSTOR(April2009)(Learnhowandwhentoremovethistemplatemessage) Photoengravingisaprocessthatusesalight-sensitivephotoresistappliedtothesurfacetobeengravedtocreateamaskthatshieldssomeareasduringasubsequentoperationwhichetches,dissolves,orotherwiseremovessomeorallofthematerialfromtheunshieldedareas.Normallyappliedtometal,itcanalsobeusedonglass,plasticandothermaterials. Aphotoresistisselectedwhichisresistanttotheparticularacidorotheretchingcompoundtobeused.Itmaybealiquidappliedbybrushing,spraying,pouringorothermeansandthenallowedtoset,oritmaycomeinsheetformandbeappliedbylaminating.Itisthenexposedtolight—usuallystrongultraviolet(UV)light—throughaphotographic,mechanicallyprinted,ormanuallycreatedimageorpatternontransparentfilm.Alternatively,alensmaybeusedtoprojectanimagedirectlyontoit.Typically,thephotoresistishardenedwhereitreceivessufficientexposuretolight,butsomephotoresistsareinitiallyhardandarethensoftenedbyexposure.Asolventisusedtowashawaythesoftparts,layingbaretheunderlyingmaterial,whichisthenbathedinorsprayedwiththeacidorotheretchant.Theremainingphotoresistisusuallyremovedaftertheoperationiscomplete. Inthegraphicarts,photoengravingisusedtomakeprintingplatesforvariousprintingprocesses,reproducingawidevarietyofgraphicssuchaslettering,linedrawingsandphotographs.Photogravureandscreenprintingareexamplesofsuchprocess. Thesameprocedureisusedtomakeprintedcircuitboards,foil-stampingdiesandembossingdies.Itisalsousedtomakenameplates,commemorativeplaquesandotherdecorativeengravings.Itcanbeusedtomakeflatsprings,levers,gearsandotherpracticalcomponentsthatwouldotherwisebefabricatedfromsheetmetalbycutting,drilling,jigsawingorstamping.Averyhighdegreeofprecisionispossible.Intheseapplications,itisproperlycalledphotochemicalmachining,butthetermsphotochemicalmilling,chemicalmillingandphotoetchingaresometimesused.Asimilarprocesscalledphotolithographyisusedtomakeintegratedcircuits. Contents 1Methods 2History 3Seealso 4References 5Furtherreading Methods[edit] Onemethodofphotoengravingproducesashallowdepressioninthemetal.Thisisusedforintaglioprintingplatesorfordecorativepurposes.Itisalsothesamemethodusedforprintedcircuitboards.Theengravingisusuallymadeincopperorbrass.Theprocesscanbedoneinopentraysbutismuchmoreeffectiveiftheetchant(oftenferricchloride)issprayedontothemetal.Whenferricchlorideisusedastheetchant,nometalpartsotherthantitaniumcanbeusedintheetchingequipment.Decorativeengravingisoftenfilledbyspray-paintingthensandingtoremovethepaintfromtheraisedpartsoftheengraving. Anothermethodproducesadeepengravingwithslopedshoulders.Inthismethod,themetal(usuallyzincormagnesium)isheldfacedownandamixtureofnitricacidandasoap-likeoilissplashedontoit.Astheacidetchesthesurface,theoiladherestotheedgesoftheexposedarea.Thisprogressivelyreducestheareabeingetched,resultinginaslopededge;asingledotwillendupasacone-shapedmoundprotrudingfromtheetchedarea.Thismethodisusedforprintingplates(theshouldersupportstheprintingsurface),foilstampingdiesandembossingdies.Decorativeengravingsmadebythismethodmaygothroughasecondprocesstoproduceadecorativebackground.Theraisedpartsandtheirshouldersarepaintedwithanetchant-resistantmaterialandapatternofetchant-resistantmaterialisappliedtothedeeppartsoftheengraving.Theresistforthebackgroundmaybeanotherphotoengravingormayberandomlysplashedon.Theengravingisetchedagainforashorttimetoproducearaisedpatterninthebackground.Decorativeengravingsofthistypemayalsobespray-paintedandsandedasinthepreviousmethod. Intraditionalprintshoppractice,aspecialvery-large-formatcameraisusedtoimagethesourcematerialeitherdirectlyontothephotosensitivecoating,orontoasheetofphotographicfilmwhichisthendevelopedandcontact-printedontothecoatedplate.Inlarge-scalecommercialprinting,computer-drivenoptoelectronicequivalentsbegantoreplacethesemethodsinthe1970s.Inthecaseoflinecuts(graphicsinsolidblacksandwhiteswithoutgradationsofgrayorcolor),thephotoengravingisdoneonzinc,andtheresultiscalledazincetching.Inthecaseofhalftonecuts,theworkisdoneoncopper.Thehalftoneeffectisaccomplishedbyphotographingthesubjectthroughawireorglassscreen,whichbreakstheimageupintoapatternofdotswithsizescorrespondingtothelocalbrightnessoftheimage;thelargerdotscreatethedarkerareas,thesmallerdotsthehighlights.Thefinerthescreen,thefinerthedetailpossibleintheprintedproduct.Halftonesmadewithascreenhaving65linestotheinchareconsideredcoarse.Thosehaving150linestotheinchareconsideredfine. History[edit] Theoldestknownprintmadefromaphotoengravedplate,byNicéphoreNiépcein1825.Itreproducesa17th-centuryFlemishengraving.Niépcecalledtheprocess"Heliography". Aprintmadein1907fromaphotoengravedplate.ItreproducesasketchofParga'scastlemadebyLudwigSalvator. Thefirst[citationneeded]photoengravingprocesswasdevelopedinthe1820sbyNicéphoreNiépce,whichusedphotoresisttomakeaone-offcameraphotographratherthanaprintingplate.Hisusualtestsubjectswerepaperprintsofconventionalengravings,andexposurewasbycontactunderdirectsunlightratherthanbytheuseofacamera.Severalmetalsweretriedfortheprintingplate,aswellasglassandlithographicstone.Hisfirstsuccesscamein1822.[1]Theearliestknownsurvivingexampleofapaperprintmadefromoneofhisphotoengravedplatesdatesto1825andreproducesa17th-centuryengraving.[2] NiépceusedBitumenofJudeaasthephotoresist.Initiallysolubleinvariousspiritsandoils,athincoatingofbitumenhardens(polymerizes)whereitisexposedtolight.Theunexposedpartscanthenberinsedawaywithasolvent,baringtheunderlyingmaterial,whichcanthenbeetchedtothedesireddepth.[1]Niépce'sprocesslaydormantformanyyears,butitwasrevivedinthe1850sandbitumenwaswidelyusedasaphotoresistfarintothe20thcentury.[citationneeded]Verylongexposuresinbrightlightwererequired,butbitumenhadtheadvantagethatitwassuperblyresistanttostrongacids.[1] Theuseofphotoengravingforahalftoneprocessthatcouldbeusedtoprintgrayscalephotographicimagesdatesallthewaybacktothe1839introductionofthedaguerreotype,thefirstpracticalphotographicprocess.Thedaguerreotypeimageconsistedofamicroscopicallyfinegranularstructureonthesurfaceofasilver-platedcoppersheetthathadbeenpolishedtoamirrorfinish.Methodsweresoondevisedfordifferentiallyetchingtheimagegrainsandthegroundsothatthedaguerreotypecouldbeusedasaprintingplate.Insomeinstances,verypleasingresultswereobtained,butexceptionalskillandcarewererequiredandtheveryfinestructureoftheimagelimitedtheusefullifeofeachplatetoafewhundredprintsatbest. HenryFoxTalbotisusuallycreditedwiththefirstworkableprocessforconvertingagrayscaleimageintoavaryingstructureofstarkblackandwhitethatresultedinareasonablydurableprintingplate.Aswithotherearlyhalftoneprocesses,theplatecouldnotbecombinedwithordinarytype,soforinclusioninabookorperiodicaleachimagehadtobeprintedseparatelyandeitherboundinortippedinwithanadhesive. FredericE.Ivesisusuallycreditedwiththefirstcommerciallysuccessfulprocessthatwascompatiblewithordinaryletterpressprinting,sothathalftoneblockscouldbeprintedalongwithblocksoftextinbooks,periodicalsandnewspapers.Hisprocesscameintowidespreaduseduringthe1890s,largelyreplacingthehand-engravedwoodandmetalblocksthathadpreviouslyservedtoprovideillustrations. Asinmanyotherfieldsofinvention,thereareconflictingclaimsofpriority,instancesofsimultaneousinvention,andvariouslynuanceddefinitionsoftheterminology,sosortingoutthemeritsofthe"first"claimsmadeonbehalfofthemanyinventorsinthefieldofhalftonereproduction—notinfrequentlybiasedbynationalisticsentiments—canbeveryproblematic. Seealso[edit] Photogravure References[edit] ^abc"1819-1824—Inventionofphotoengraving".NicéphoreNiépceHouseMuseum.France.NiépceandtheInventionofPhotography.Archivedfromtheoriginalon2021-05-02.Retrieved2021-06-30. ^"Noticebibliographique:ChevalavecsonconducteurImagefixe :photographie/NicéphoreNiépce".BibliothèquenationaledeFrance.BNF 42708962x. Furtherreading[edit] HarryJenkins,StephenH.Horgan,FredericEugeneIves,ContainingPracticalInstructionsforProducingPhotoengravedPlates...,Chicago1902. 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