Hi Madelyn! I am very confused about the difference between unit weaves and block weaves. We just had a guild program on block weaves and the presenter seemed to use those two words interchangeably. Can you clarify?
It's making me smile to get this question since I just finished recording a DVD on block weaves. I sure hope I make this very clear in the video, but here goes a short version. The first definition you'll need to understand is the definition of block weaves. These are weaves in which the same warp and weft threads can make two different-looking interlacements, one that we identify as pattern ("figure") and the other as background (think about how you see a rose motif in some overshot drafts on a background of plain weave). Overshot is a block weave, and so is Atwater-Bronson lace and summer and winter and many more.
Some block weaves, however, make the pattern and background interlacements with independently functioning threading and treadling "units." These units all do the same thing as each other to create either the pattern interlacement or the background interlacement, so you can thread many units of the same block next door to each other and weave many in succession (or only one in each direction).
Summer and winter and Atwater-Bronson lace are like this. You can design a large center table or a heart or a large diamond of lace or summer-and-winter pattern-weft floats against a background, for example. But with overshot, you are limited to the potential width of the pattern-weft float in determining the width of any block. With unit weaves, all the interlacement takes place within each unit. With overshot, the pattern weft doesn't interlace in the block at all; it just passes over it. So overshot is a block weave but not a unit weave. Atwater-Bronson lace and summer and winter are unit weaves. All unit weaves are block weaves, but not all block weaves are unit weaves. Unit weaves can be used without limitation with profile drafts (block designs), whereas non-unit block weaves have certain limitations (overshot, crackle, M's and O's, spot Bronson).
I hope the video will make all of this easy to understand!