A centered wick is easier to achieve before pouring wax than after it starts to cool. Once the wax is in the container, any tug on the top of the wick could cause the wick tab to shift on the base or for the upper part of the wick to lean to one side. That’s important because an off-center wick could cause uneven heating, an uneven melt pool, or an overly hot spot near the side of the container. Consider centering your wick as part of the container prep, not a final adjustment while the candle cools.
Start with the empty candle jar. Position the wick tab as close to the center of the base as possible, and look down the container to see if the wick is straight. Seeing it from above will show you mistakes much better than looking from just one direction. A wick sticker or other appropriate way to hold the wick tab in place can help. Make sure you press it securely onto a clean, dry surface to decrease the chances of it shifting when you add warm wax. You can also test out how securely the wick is holding by gently tugging up on the wick before adding wax. The tab should not move along the bottom.
Also secure the top of the wick. A wick centering tool, holder, or other appropriate method should keep the wick straight without putting too much tension on the wick. Too much tension could pull on the wick tab and make the lower attachment less secure. Too little tension could allow the wick to bend or shift as you pour the wax. You want the wick to run in a straight line from the tab to the top of the container. If there’s a slight curve, use the holder to correct it while the container is empty rather than expecting the wax to hold it in place while cooling.
When you’re ready to pour, take care to direct the wax away from the wick to keep it from shifting. In particular, avoid a fast stream of wax being directed straight at the wick, which could easily cause the wick to shift, especially in a small container. Pour slowly into the space next to the wick and pay attention to the upper portion of the wick as you fill. After the pour, look at the wick from above again. If the wick moved slightly, you can make a tiny adjustment while the wax is still completely liquid, but don’t keep pushing and pulling the wick. It’s possible to disrupt the wax surface and dislodge the tab at the bottom.
To practice centering your wick, set up several empty containers and attach a wick to each one. Add the wick centering tool, look at the wick from above, and assess your results. Try tapping or moving the containers like you might when placing them on a table, and see whether the wicks shift. Practicing without pouring wax allows you to focus on your wick centering technique without worrying about controlling temperature or pouring wax. When you feel comfortable doing it, try it on a small test candle and notice whether the wick remains centered during the cooling process.
Once your candle has cooled, take a look at your wick before trimming it. Notice how far the wick is from the side of the container on all sides. If you notice a slight deviation, see if you can pinpoint what moment during the process caused it to shift: during the attachment, the pour, or when you moved the container. On the next candle, try to address that specific step in the process. A wick that remains in the place you put it is a good indication that your technique is improving.