Trim when the pot holds its shape during handling and the tool can remove controlled shavings. Before turning it upside down, inspect the inside floor and plan how much clay can come away beneath it.
Read the clay condition
Pressing attachment clay against the pot should not deform it. Smearing under the tool suggests the clay is still too soft; dry powder calls for stopping and reassessing the clay and tool. Leather-hard covers a range, so the condition at the base matters more than elapsed hours.
A thick base can remain soft after the rim has firmed. Check both. Turn or protect the piece as appropriate during drying so that the parts you intend to trim do not lag far behind an increasingly brittle edge.
Locate the floor and choose a foot
Look inside before inverting the pot. Recall the floor depth you measured when opening and note the shape of the interior curve. If you made no measurement, be conservative. A heavy feel alone cannot tell you exactly where the spare clay is.
Sketch the foot ring relative to the interior curve. A narrow ring gives a broad bowl a different stance from a wider one. Mark the intended outline before deepening a groove that limits the remaining choices.
Secure the inverted pot
Rest the pot on an appropriate clean support that will not damage the rim. Center it carefully and secure it using a suitable trimming method. Clay lugs should hold the form without distorting it. An irregular or delicate rim may require a different support arrangement.
Turn cautiously to confirm that the piece stays secure before presenting a tool. If it shifts, stop the wheel and fix the attachment. Adding speed to an unstable setup increases the problem. Keep the work area clear of objects that a displaced pot could strike.
Cut and check the bearing surface
Brace the tool and take controlled, light cuts. Establish the outside of the foot, then work on the recessed area while preserving the planned floor. Avoid repeatedly deepening one narrow track. Tool bounce can come from attachment, clay condition, tool angle or speed; inspect those factors rather than pushing harder.
Pause to check the profile and remaining allowance. Finish the bearing surface evenly so the foot sits as intended, then remove the pot and inspect it upright. Look for a foot that supports the form without a sharp or ragged contact edge.
Collect trimmings for damp cleanup before they become dry debris. Keep a note of the original floor allowance if this is a practice piece; it will help you plan how deeply to open the next one.
Questions about this topic
Must every thrown pot have a trimmed foot ring?
No. Some forms use a finished flat base or another deliberate underside. Trimming is a design and weight-distribution decision.
Can I trim bone-dry clay?
That is not the normal beginner trimming stage. Dry clay is more brittle and dusty; work at an appropriate leather-hard condition and seek instruction for unusual processes.