Many people struggle when trying to learn how to smooth polymer clay, even when it comes to blending one section of clay to another (such as a limb to a body of a figure).
I will try to give you some tips on how I've best come to do these tasks through the years so far. Firstly, please watch this quick little video:
If the video doesn't play, watch it on Youtube here.
Blending and smoothing polymer clay is very important, not just to make something look better, but also to make the sculpture more structurally sound. As mentioned in the video above, if you simply press clay into another piece of clay and bake it, it stands a good chance of breaking off. To really secure the clay, you need to blend the clay and smooth it.
To blend the clay, very gently run your fingers over the clay that you want to blend. You want to shift the edges of the clay to blend it into the rest of the sculpture without distorting the entire shape. For example, if you're trying to blend the arm into the body like in the demonstration above, you don't want to blend so much that you completely lose the shape of the arm. Try to use a sculpting tool with a smooth rounded surface. This will help you blend polymer clay easier because it won't leave harsh flat lines in the clay as much as flat tools do.
So what about how to smooth polymer clay?
There's many different ways you can go about it, and it's really up to you to choose the best method that works for you.
I personally like to use my fingers to smooth over the clay as I work (as demonstrated in the video above). However, this does require practice as you need to handle the sculpture in such a way so that you do not keep squashing the areas you have just smoothed. Also, you need to be able to keep your hands in good condition, very smooth and soft; so it may be difficult if you do activities such as gardening.
Another option is using products such a Prosculpt smoothing oil or Sculpey Clay Softener. Simply apply a small amount to a soft paint brush and gently stroke it over the clay. This will remove minor imperfections like shallow creases and fingerprints. Be sure that the bristles on the paint brush are soft, or they can leave little grooves across the clay. This is the most recommended option if you're a beginner. You can use baby oil, but I do tend to find that this can make it a bit too greasy to work with if you don't use the right amount. Also, you run the risk of it not fully absorbing and causing some issues when you try to paint the doll later on.
It's generally most recommended to use the product that's designed for the clay. Prosculpt smoothing oil and Sculpey Clay softener can usually be found on eBay or most craft stores that sell Super Sculpey Polymer Clay.
You can also try sanding your sculptures for more major imperfections across the clay. Use a very fine grit sandpaper and then work down do the finest grit wet/dry sandpaper. This should remove any problems. However, be very careful how much you sand the sculpture. If you sand away too much of the polymer clay, you can cause cracks and show up separations in the blending. You want everything to stay seamless, so you really want keep any sanding as minimal as possible, and be gentle when you're handling the figure.
I hope I have helped you to learn how to smooth polymer clay. Remember, while it's good to have a very nice and polished sculpture, don't forget to have muscle and bone detail. Sometimes you can take smoothing and blending so far that you lose all your wonderful hard work. Be sure to keep what's important!