3c Deep Violet, "China Clay" Experimental Paper (333 var). Bottom imprint and plate no. 4927 block of six, much darker shade of paper which at one time constituted the "China Clay" paper, bottom right stamp slight internal crease, otherwise Fine-Very Fine, with 1992 P.F. certificate as No. 333a "China Clay", the P.F. will no longer certify this variety so it is offered as is -- although there is an argument between "scientists" over what constitutes China Clay paper, the obvious experimental nature of this rare paper variety has been known for 80+ years -- ex Wampler (where it realized $6,000 as No. 333a)

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