Thanks, it is the thought that counts and besides the tortoise always reaches there in the end.
I just started collecting and thus my knowledge is gleaned from the internet and some stuff that people are willing to share with me, so take it for what it is worth.
Zisha, translated to "purple clay". Depending on the context by the speaker, it can include all the types of clay in yixing that are used to make the teapots. Thus i have heard taiwanese vendor who told me that his pots were made from zisha imported from yixing. Others take it to mean zini, a specific clay within the family.
I have no experience with yixing.com and cannot comment on their pots. In general the amount of pots that are in existence exceeds the amount of clay available to make such pots. This led some to conclude that the clay was actually added with mud (perhaps) to increase the quantity or made with clay that are not found in yixing.
As a result, you can go to yixing, china and inadvertently buy pots that were made with clay from other provinces. Or you can buy an expensive pot that were made using clay mixed with mud or sand or other additives. One solution is to get from a reputable vendor.
There is one site that i went to admire the pots - deeho.com. (However this is not an endorsement to buy from deeho as firstly i have not bought any from them and secondly i can get some of the pots cheaper).
It is possible that the pots are made with good quality clay because these pots were reportedly sourced from the actual potters themselves. However you should check the authenticity of the pots in terms of the maker - some of the potters have apprentices, studios or family members who made the pots too. It is possible that the potter may pick the best pots made by those around him/her and put his seal on it.
Honesty on the part of the vendor as well as the potter is your best safeguard. For example over at deeho there is a potter by the name of Wu ChengJing. If you look at the detailed description, for some of the pots it stated that it was designed by her and handmade by artists of her workshop. Such candid disclosures are rare.
Now regarding your yixing teapot. You might like to do the following test on your teapot - fill it with hot water, put back the cover and carefully smell along the rim. It should smell clean. Next put the teapot on a pot of water, the cover alongside it. Fill with water with sufficient quantity to just cover the teapot. Boil the water. When it reached boiling point or close to boiling point, put the fire to the lowest flame possible for about an hour. (Note under no circumstances let the teapot or its cover move or float in the water as they may knock against each other or the sides of the container). Let it cool. The next day smell the interior of the dry pot. It should smell clean. The clean smell meant that it is likely the pot is made from genuine clay without toxic materials.
You can then proceed to use the teapot (with a fair sense of reasonableness that the teapot is usable), for the type of tea you choose.
So Tortoise, you know as much as me now
However do doublecheck as there are plenty of people here and elsewhere who have far more knowledge and experience.
