If you have various pottery components to your oil lamp, they should be attached to the main body when the body is at leather hard. Score and slip, then attach components firmly.
For my oil lamp, I marked out three equidistant spots centered on the bottom of the pot, then scored, slipped, and welded the elephants into place. I immediately turned the lamp over and pushed firmly but gently downwards. This firmed the attachment up even more, and also flattened the elephants' bottoms so that the lamp would stand steady.