These saws are quite inexpensive and they make impressive claims on what you will be able to cut. But, things are different in practice! First, it is a real challenge to get the diamond wire to stay in the saw, it pulls out easily. It is not possible to turn the thumb screws tight enough with your fingers, you will need to use a pair of pliers. Then the challenge is tightening them enough to hold the wire securely, but not so tight you strip the threads. Once the wire is in securely, be prepared to make slow progress. This type of cutting is normally done by a machine that loops the wire continually, for hours. To cut this soft terra cotta piece took about 15 minutes! It was fired to about cone 010. Cutting stoneware or porcelain would likely be impossible. Even bisque ware fired to cone 06 or 04 would be harder than this. Using heavier gauge of wire would enable pressing harder, but this tool is not built heavy enough for that.
The term Terra Cotta can refer to a process or a kind of clay. Terra cotta clays are high in iron and available almost everywhere. While they vitrify at low temperatures, they are typically fired much lower than that and covered with colorful glazes.