So here goes for my attempt at clarification:
- Pima Cotton -- pima cotton is a long staple (long fiber) cotton which because of it's fiber length is perfect for making high thread count fibers. However, this doesn't mean any particular thread count, just that the fiber is a special high quality cotton.
- Pimatex -- this is a brand of tightly woven poplin made by the Robert Kaufman company. One of the "colors" is pfd white which is sold by Hancock of Paducah. It is a firm high thread count fabric that produces nice results.
- Egyptian cotton -- again, this is a type of cotton (like Pima) that used to be grown only in Egypt but now is grown in the Southeast US. It is an extremely high quality cotton (probably the best) and lends itself to high threadcount applications.
- Kona cotton -- this again is a brand name sold by Robert Kaufman and is a relatively low threadcount but has good firm threads. It may be made from pima cotton.
- Cotton Lawn -- this is a very soft, finer quality cotton which is the basis for the Hoffman batiks for the most part. It is most likely made from high quality pima cotton as well.
- Cotton Sateen -- this is a weave of cotton. The highest quality sateens are made from pima or Egyptian cotton and are combed cotton. It is almost impossible to get the highest quality here in the US but a couple of manufacturers are making a decent sateen these days.
- PFD or Prepared for Dyeing -- this is fabric that doesn't have any finishes that interfere with the dyeing process. Some of these finishes might include permanent press or optical brighteners. Being labelled PFD does not guarantee that it will give you the wonderful bright crisp colors that you might like. This requires that the fabric also be mercerized.
- Mercerized cotton -- this is cotton that has been treated with a very strong base during it's processing (seems to me I read that it was lye in combination with some other things). This process causes the fibers to appear to hold more color because of the surface. You can kind of tell if a pfd fabric is mercerized as it has a very slight sheen to it when held in the light. I have found many fabrics not labelled as pfd but which were mercerized and dyed beautifully. I have found others identified as pfd which don't dye well at all!!
There are also many different weaves and thread counts of cottons. I cheated above as sateen is a weave as well as a "finish" which makes the surface highly reflective.
Old damask in many cases makes for a great dyeing surface (check out those thrift stores). Also, if you can find those sheets that were all cotton and made back in the 40's and 50's, they tend to be mercerized as well. Before the advent of optical brighteners, mercerization was the process used to insure you had nice bright whites!
Many times you can find sateen or Egyptian cotton sheets made in India or Pakistan that contain no optical brighteners and therefore dye beautifully. I have found that optical brighteners make the white fabrics look vaguely pale, pale lavender under the store lights. You have to look really, really closely. I have found for some reason that the sheets made in Thailand or Malaysia almost always have optical brighteners!
My personal opinion is that viscose (NOT acetate) rayon dyes more beautifully than anything else. It rarely if ever has any finish on it but is hard to find except from pfd vendors in 100 % rayon. You have to be careful with it when it is wet though as it tends to be a bit fragile. However, any combination of rayon/cotton or rayon/linen that you can find will dye beautifully as well, even if not pfd. When you get the mixes, be careful that there are no permanent press finishes though. I love the 55% rayon, 45% linen fabric from Joann's. It is great for clothing and dyes wonderfully.
Silks dye wonderfully using the same processes. Lighter weight silks will just not hold as much color so a 3mm silk will not be as colorful as a 10mm silk just because there is not as much fiber to dye. Charmeuses and silk blends (with rayon, cotton or linen) dye beautifully using the MX dyes and soda ash. Pure silk can be dyed beautifully with MX dyes using vinegar or citric acid as well.