hobin wrote:I'm not really versed in F1 shuiping... what's the difference between 6-and 4-character pots? (I suppose the 6-character ones are rarer, I usually see plenty of yixing zhongguo seals)
very good question

there are many possible answers and many whom know different versions of the answers, but as far as my research goes (which is still on going) here's a quick summary
the 6 characters usually refer to 荆溪惠孟臣制,宜兴惠孟臣制 etc, where Jingxi = Old name for Yixing, Hui Meng Chen is the guy whom inspired the wave of small pots that many potters still make small pots in his name. these small pots were so instrumental in driving gongfu cha that there are old sayings.. pot must be mengchen, cup must be ruosheng.
The earliest 6 character appeared in Late Qing to ROC, i.e. 三点溪
then towards 30-50s Peng Gai Series there is 宜兴惠孟臣制,荆溪惠孟臣制(4脚),荆溪南孟臣制。
all these predated Factory 1, but when F1 was established in '58, some of these type of seals were incorporated into the factory work.
in the 58-60s, more variants of the 6 character sealed appeared, namely 大字溪,小字溪,川溪,along with the use of 4脚溪,南孟臣。these seals are rather prim and proper, neat, with cracks forming in them over usage, allowing people at later dates to quickly identify through these crack patterns, and supposedly to determine whether they are end 50s or mid 60s.
with the cultural revolution (66-76), and the need to distance themselves from historical/cultural elements, and to drive a more nationalistic idealogies, Zhong Guo Yixing in 4 character seal was coined to replace any mention of meng chen.
Taiwan was quite into Yixing pots then, due to their unfriendly connections with china then, there were mention of people grinding off the Zhong Guo Yixing seal at the base of the pot just to enable import, some were painted away.
After the CR, when relations became slightly more cordial, there was a reversion to 6 character seals which doesnt contain the Zhong Guo Word for easier import/exportation. Correspondingly, the green round stick with the "made in china" words on it was first issued around '77 up to '82, importers could decide whether to keep it or to remove it. During this era, there are also new 4 character seals created, i.e. if the author is Wang, the pot seal will be 荆溪王制 (Jing Xi, made by wang). Many of this style of 4 character seals are in taiwan. all these occured in parallel with the 4 character Zhong Guo Yixing stamp, and into the Fang Yuan label eras from '83 onward, makers started stamping their own names etc, and we can summarize here that in the 80s, seals are really diverse. But more interestingly the 6 character of the 80s is no longer in the prim and proper scripts of the 60s. they are rough, coarse, the dimensions are not as standardized, can be narrower, words are jagged.
Zhong Guo Yixing seals also has its own complications, a 6/4 seal seen in the 60s was seen re-used in end 70s, and said to be in some parts of 80s.
in the early 2000s, there was also a version of a re-carved 60s 4-leg seal, that was used on hong ni pots that were of a close clay quality of that of the 60s, xcept the firing was different. the person whom carved the seal is on face book and is actively involved in the recent publication on shuiping hu. he did leave some hidden flaw in the seal so that it can be easy to distinguish a pot of the re-carved seal vs an original 60s.
complicated no?

but it will clear up really soon once you start playing.. reading, and discussing