9第9章 (2/2)

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hequalityandtextureoffinishedproducts.Theteachertoldusthatqualifiedclaymustbefineandparticle-free,uniforminmoistureandhighlyplastic;otherwise,finishedwaresarepronetocracking,bubblinganddeformation.Ifirstsievedrawclaytoremovegravelandimpuritiesmixedinside,thenconductedrepeatedwedgingandpugging.Attheverybeginning,mywedgingposturewasstiffwithunevenforce,leavingmassiveairtrappedinsidetheclay.Undertheteacher’sinstruction,Imasteredthecrosswedgingmethodtoexpelinternalairbubblesviarepeatedfolding,pressingandkneading.Aftermultipleroundsofpractice,Ihandledtheskilladeptly,andtheprocessedclaybecamecompact,smoothandsoft,reachingthestandardforcasting.
  

  

  
Withclaypreparationfinished,weproceededtothecoresessionofthistraining:slipcastingwithplastermolds.Plastermoldsfeaturegoodairpermeabilityandmoderatewaterabsorption,makingthemthemostwidelyadoptedmoldmaterialforceramiccasting.Beforeoperation,Ithoroughlycleanedandair-driedmoldstoavoidresidualcontaminantsimpairingtheflatnessoffinishedwares.Afterwards,moldswereassembledandfastenedwithclampstopreventslipleakageduringpouring.Next,slipwasblendedaccordingtopreciseproportionswithstrictcontroloverconcentration.Overlythickslipleadstounevenwallthicknessofgreenware,whileexcessivelythinslipresultsinloose,incompletemoldedbodies.
  

  

  
Oncetheslipwaswellblended,Ipoureditslowlyandevenlyintomolds.Fastpouringwouldgenerateabundantairbubbles,sosteady,gentleflowwasmaintainedthroughouttheprocess.Afterfillingthemoldscompletely,westoodbyfortenminutes,allowingthewater-absorbentplastertoformanevenclaylayerattachedtotheinnermoldwall.Excessslipwasthendrainedoff,followedbyanotherrestingperiodforpreliminaryshapingofgreenware.Thisproceduredemandsimmensepatienceandprecisecontrol.Duringmyfirsttrial,improperrestingtimecauseduneventhicknessatthebottomandjaggededgesafterdemolding.Identifyingthisdefect,Irepeatedlyobservedtheinstructor’soperatingrhythmandrecordedcriticalparameterssuchasrestingdurationandpouringspeed.Afternumeroustrialsandadjustments,Ifinallyproducedneatlyshapedgreenwarewithuniformwallthickness.
  

  

  
Afterpreliminaryshapingofgreenwarecametrimmingandair-drying.Leather-hardgreenwaremarkstheoptimaltrimmingwindow:atthisstage,claypossessessufficienthardnesswhileremainingmalleableforshapingrefinement.Iusedtrimmingknivesandscraperstocarefullysmoothroughedges,airholes,concave-convexdefectsandjointseams,polishingoutlinesandcontoursformorefluentoverallforms.Trimmingcompleted,directfiringwasforbidden;greenwarehadtobenaturallyair-driedinwell-ventilatedcoolareaswithoutdirectsunlightexposure.Rapidmoistureevaporationundersunlightwouldinevitablytriggercrackinganddeformation.Followingtheteacher’srequirements,Iplaced