I was working on printing an edition yesterday and I had plenty of time to think about how the ink, plate and tarlatan (or your hand) interact during the process.
When you first start to wipe after applying the ink (I use a silicon spatula for that) you are mostly using physical means to remove the ink. I like to think of the tarlatan as ‘slicing’ the ink off of the plate. I am using a small swirling motion driven from the wrist. It is a little like scrubbing, but with very little pressure. The tarlatan is formed into a ball with a single smooth layer pulled over the bottom where it contacts the plate. I like to use a piece about the size of a baseball, although many people like a larger ball. As the ink is sliced off, the weave of the tarlatan will start to get plugged. When this happens, the dynamic changes and the ink starts to smear around instead of being removed quickly. Time to refold to bring a fresh area to bear. If you continue without refolding, you will find yourself pressing harder and harder and getting less and less ink off. Pressure is your enemy when wiping as it causes the tarlatan to dip down into the image areas an pull more ink on to the surface, making things worse.
You fairly quickly get to the point where there is a thin film of ink left. At this point the dynamic changes. It seems that the ink to ink affinity becomes the driving factor. Though it seems counter intuitive, reducing the pressure and moving more quickly makes the wiping more effective. As the tarlatan glides by, the ink on the plate sticks to the ink on the tarlatan and it rips off of the plate. If the ink on the tarlatan is too thick, the opposite happens and the ink film tears, putting down as much as you pick up. When this happens, refold. If your wipe is gentle enough, you do not have to worry about pulling ink up out of the image. (Unless of course, there is something wrong with your ink consistency).
When the plate is getting pretty clean with some smearing out from the darker areas, I switch to my hand. At this point the motion changes: I lock the wrist and the motion is from the elbow. Gently, quickly wipe. Just caress the plate. I wipe in toward the image, drawing the ink in rather than pulling it out. Sometimes I draw towards my body using the heel of my hand. Other times I use the pad at the base of my thumb and push away. Again, the interaction is chemical. The ink wants to stick to your hand more than it does to other ink or the plate. Wipe the edges of the plate with a rag and wipe your hand periodically.
Your touch gets lighter and lighter. Change the plate direction to keep yourself wiping in towards the image or parallel to an edge in the image. Those little wisps of ink will disappear.
Sometimes you may get some ‘lumps’ that resist wiping. I think that these are areas that get burnished by the friction of the wipe. I seem to get them when I have left too much ink on when I started hand wiping. A touch with the tarlatan should make them go away.
Like any skill, you only get better with practice, practice and more practice. Observing carefully as you go can only help.