Texture marks can look quite different on a loose piece of clay compared to when you try them on the side of a dish. The flat surface allows you to press your stamp evenly, while the same tool can distort the edge of a curved plate, cause a dent in a shallow bowl wall, or result in one side of your texture being deeper than the other. That is why creating test tiles is recommended before beginning your dish.
The purpose of a test tile is not to create a new piece of work. Instead, a practice piece of clay allows you to experiment with certain details so that you do not run the risk of ruining your actual dish. You can use a tile to answer questions such as: Is the clay too wet when you press your texture stamp? Is one layer better than two, or a repeating texture mark? Is the line from your needle tool or carving implement too wide, or are you dragging excess soft clay with it? All of these details are much easier to test on a practice piece than when your piece has been smoothed and is ready to receive texture details.
Create a few small practice tiles by simply rolling some extra clay and cutting a few rectangles or circles. Make these slightly thicker, so they don’t buckle too easily when you push your tooling tools into them. If you are able to roll your tiles from the same clay and thickness that you rolled your dish, this would be a very good comparison. Your tiles should be a few millimeters thicker than your dish wall thickness. If you do not use a thick practice tile, there is a risk that the thin tile could be different than the sturdier base of your dish, or it could not reveal any issues you will encounter when you are texture decorating the thinner walls of a shallow bowl.
Texture practice can be done at several stages of drying. Test one tile with your texture stamp while the clay is wet, then wait for the clay to firm a little and try your texture stamp again on another piece. Next, try using your needle tool or carving point on yet another practice tile at leather hard. You will notice that the imprint will be quite deep, and the details will be a bit soft in the soft clay. As the clay firms, your detail will appear more precise, although the clay is now at a greater risk for cracking or chipping from your tooling tools.
Using water on the practice tile can also change your texture mark, such as using a slightly damp sponge to smooth out your practice clay before applying your mark. Too much moisture can lead to soft, smearing clay, or the clay sticking to your tool. If the clay is lifting when you remove your stamp or texture tool, the surface may be too wet and should be left to firm slightly. If the needle tool or carving implement is not cutting the clay as cleanly and the edges are crumbling, your clay surface may be too dry or you may be applying too much pressure. Test tiles help you discover the correct consistency to get great texture details, without ruining the surface of your dish.
Finally, try creating your texture marks on your practice tile in the same configuration as you are imagining on your finished work. A single texture mark in the center of a tray feels very different than a repeated texture mark around the rim. A single, delicate line of texture can look calm when there is a fair amount of space surrounding the line, or it can look crowded when it is used next to underglaze colors or more texture marks. Creating your texture practice tiles at the intended size and pattern will help you see the rhythm, spacing, and pressure marks of the design, as opposed to just a single mark in the middle of a piece.
Once you have tested your texture marks, place your practice tile next to the piece, and compare both surfaces. How wet or dry is the dish, how firm, and how curved, compared to your practice tile? If the surfaces seem different from one another, make the necessary adjustments before using your first mark. Surface texture is intended to compliment the clay and the form of a piece, and can take time to find the perfect texture mark for your specific dish. Testing on a practice piece can avoid muddy texture marks, distorted walls, or decorations that may seem to not fit your work.