Maintaining consistent weft tension with the use of bubbling, as illustrated in the image below, is one of the most important aspects of tapestry weaving, lest your warps become too close together or too far apart. One of the most common issues for a beginner tapestry weaver is encountering these issues, and the scariest scenario is when your warps get so close together that you can no longer create weft-faced cloth while weaving. This means your warps are showing through your weft! The technical name for these bits of warp showing through is ‘lice’. But, if I’m honest I rarely use that term because it grosses me out.
When your warps get too close together they cause your weaving plane to no longer being even; the area where your warps are too close together will appear as a mound along your weaving area. It will also result in your tapestry's 'edges' or selvages to change and your tapestry as a whole will appear to be narrowing. That is because no matter where your tapestry is getting smaller in width (on the inside or on the edges), your selvages will appear to slant inward.
So, let's talk technique. When weaving tapestry one should always create bubbles with the weft once it is inserted between the warps. If you do not bubble your weft enough your warps will become closer and closer together, getting worse with each offense. Conversely, if you bubble too much your warps will become further apart. In both cases, these issues are usually isolated to one area of your weaving. Interestingly, wherever the issue occurs it is changing the shape of your tapestry. So, to maintain the appearance of straight and square selvages, you want to stay on top of your weft tension, and find and stick to a happy medium with your bubbling practices.
In tapestry, woven weft should slightly wrap around the warps it is weaving into, hugging it. The purpose of bubbling your weft as you weave, as shown in the illustrations above, is to create the perfect amount of weft to allow for this hugging to occur. The weft should hug halfway around the warp, as opposed to lay in front/behind it. Too much weft will cause the warps to push apart, not enough weft will draw the warps together.
Here’s how to remedy these issues. If you are finding that some warps are getting too close together, bubble more in that area of weaving. This usually takes quite a few picks of weaving before the problem is solved. The key here is to make sure you don’t let the problem get too bad before you begin to troubleshoot it. So, as you weave keep a close eye on the spacing between your warps. If you are at the point where your warp is showing through and you have a hill to contend with, just keep with your bigger bubbles in that area, stuffing more weft between those warps in each pick, until the issue is resolved. It will take some time.
Conversely, If you find that some warps are getting too far apart, make smaller bubbles or no bubbles at all every time you pass over the area of the issue, until the problem is resolved.