
Here are some examples of my creations with this effect:

In this case, I start with a red clay on which I apply, during the degourdi or on raw piece, a manganese oxide juice. The application of this juice on a piece with reliefs will allow to highlight them.
Manganese oxide juice:
Before going any further, let me explain what a juice is. Nothing complicated, it is simply a liquid (water) and a metal oxide (here manganese). I don't have a concentration to give you. However, the more oxide you put in your water, the more it will be charged. Therefore, when you put down your preparation, you will have less to put. Warning: this may seem like a good idea, but I think it is easier to go through several times with a low concentration.
Explanations:
The juice will settle in greater quantity in the hollows. The water being absorbed by the shard, will therefore leave more oxides in the hollow parts than in the reliefs, which allows to create a contrast between hollow parts and reliefs and to bring out the details on the piece.
Manganese oxide leaves a black color after firing.
The concentration of oxide in the preparation allows to bring more or less marked tints. The fact of passing several layers of this juice also makes it possible to obtain an increase in the deposit of these oxides.