Crafting Material Interfaces

I used wool yarn to create a swatch of felted conductive material, testing its relative resistivity in the felting process. I also used wool rovings to create large felted strands, like dread locks—good candidates for silver thread. The former yielded a good object lesson in the properties of silver thread; the latter was mostly an opportunity for experiments with soldering and LEDs—let’s just say I know more about what *not* to do now.

If the purpose of having several projects in a semester is the chance to learn from mistakes, especially early on—well, then, this was a spectacular success.  I used great materials, and these conductive combinations have a lot of application possibilities. But I was far too cavalier about my understanding of conductivity measurement to get meaningful results (see below). Nonetheless, I got my feet wet in a number of material and electrical techniques. I’m looking forward to that SparkFun order I have coming in the mail…

For the main project, I started with this thick 100% wool yarn:

It knit up beautifully into a scarf-like strand:

And then I threaded silver conductive thread through the stitches, like this:

I made four lines of thread, leaving most of the tails long at the end to observe the changes in the threads themselves:

I was hoping to have the silver thread sufficienctly felted into the wool that it would end up invisible. You’ll see below that this didn’t work; my first mistake was these too-long stitches that wrap around the knit stitches. In the future, I’d thread them much more tightly into and through the knitted wool stitches, for a more complete, homogenous product.

Unwashed, I measured 24.3 mega Ohms of resistivity.

For the first felting, I used a rinse-and-spin cycle was to the threaded strand: The speed wash, hot/cold water, extra high spin speed. A 12 minute cycle. I measured 22 mega Ohms at this point, but the short wash hardly made a dent in the form of the piece:

I put the piece in for a second wash—again on hot/cold, but this time a full cycle (Quick Wash), with normal spin to go easier on the machine. This tightened up and blended the yarn stitches quite a bit, and damaged and frayed the strands of silver thread, as you can see at the tail end:

On the top side of the swatch, the threads weren’t visible, but this bottom side, with its overly-long stitches, still had these frayed and loose bits, not nearly as incorporated as I would have liked to see. Resistivity increased in the process, likely due to the breakdown of the thread with the vigorous action of washing/felting. I measured 33.8 mega Ohms after this second wash. Given the simple corrections that would make this a fairly coherent material, without too great a loss in conductivity, this composite is pretty promising for applications.

The second project I experimented with began with these wool “rovings”—thin strips of wool, nearly formless, like cotton candy. But with a quick soak in hot water and wool soap, and tight rolling action, they became sturdy, cigar-like strands:

With Leah’s help, I then explored some possible ways to make a whole sensor-to-actuator system here—which ended up being a tutorial in soldering and ways to handle tiny and delicate LEDs. Here’s as far as I got by 6 pm Sunday:

It was good to get this far, if just to see what kinds of material options would make this happen. Here I’m using a usually-less-desirable kind of conductive thread—it has frayed and “hairy” edges, meaning its carrying power is more unstable. For motion-sensitive dread locks, however, that instability could be a virtue.

I’d need an insulated thread for the uninterrupted circuit, so I started piecing together the ends of the insulated thread and the metal thread with crimp beads to create a holder for a small LED. But my unpracticed skills with soldering tiny parts led only to much breakage. I’d like to finish this project just to see these work.