Modern Era Teapots and Clays (1949-1995)
The best or only way to identify authentic vs fake Yixing is to get to know existent known authentic clays. Therre are only so many existing authentic clays.
The next best rule is to estimate the age: anything made before 1995 are assumed authentic except proven otherwise. Vice versa, anything made after 1995 are assumed fake exept proven otherwise.
1) ZiNi Purple Clays
c) Culture Revolution ZiNi Purple Clay 文革紫泥 (common)
d) Culture Revolution Mixed Purple Clay 文革拼紫泥 (common)
e) Long fermented ZiNi Clay (rare)
YiXing Zisha Clay Teapot by China Yixing 77-82一厂中国宜兴绿标壶
f) Black Dotted Clay Artificially Made with manganese 黑星土 (common)
On the internet when they say they are Black Dotted Clay , they really means they are Black Dotted Clay Artificially Made with manganese .
It is still considered authentic because it was the clay of from the official 1st or 2nd factories even though it may has added chemicals (likely manganese) for the pigments. I have quite a few of this kind of clay and they are very good clays and all have very good permeability.
3) Green Clays
Republic Green 民国绿 (common, but many newly made are chemical teapots)
This clay was created by adding Cobalt Minerals, not Chemicals as commonly used today
4) DuanNi Clays (relatively rare)
mix of Purple and Green clays that exist naturally