To understand the process, one thing we are especially looking for is 'tannin' in leafs, getting out of the leaf by boiling, onto the fabric, where it will react with iron (II) sulfate what will make a grey/black print.
This process can be influenced with many parameters, one of them being the cotton used.
We have a small problem:
a) the tighter the weave/thread, the sharper the print
b) the looser the weave/thread, the better the iron-sulfate penetration.
You see the problem?
Actually we are looking for two contrary characteristics in the same fabric!
Now, to share with you my own experience, I had great results with sateen cotton which is rather losely woven and gives a nice flat surface to print on.
But even a crisp poplin will work fine, but you have to pay more attention to pre-mordanting with iron (II) sulfate and wrap it more losely around the pole.
It can be purely white, but also a light colour will do, I had good results with this bluish percale cotton (also used for sheets):
To the left the perkal cotton, to the right the regular sheet cotton:
Another possibility is to use a 'batiste', due to its open weave, you can use larger pieces of fabric to roll around your pole like a scarf!
So you see, many possibilities to play with! Check the density of your cotton and adapt the process to that: sometimes choose to wrap less fabric in order to have less layers. Or soak the fabric in a bucket of water with a teaspoon of iron sulphate (makes the fabric more gray), or rub the leaves with an iron (II ) sulfate solution before placing them on the fabric. Or as I mentioned, wrap it more losely.
Check your stash, monday we will discuss (pre) mordanting the fabric.