Monday, October 5, 2015

Fighting back moths (from yarn, not mothra)

This scenario unfolded recently where the missus rather annoyed and mildly upset that her collection of yarn has been attacked by moths. Yes, I know this is a riveting piece of news to some excluding myself until I learned more about yarn and those who knit. To start, it's been explained to me that people who knit do it because they like it, not because it's any cheaper than say buying a sweater from a store. On a recent yarn shopping trip with the missus I've learned that a good quality yarn for a sweater costs between $60 to $200 not counting the time invested. Those figures assume that you already possess the necessary tools which in this case, are knitting needles and the like. That's another thing I never realized that knitting needles come in different sizes, materials, and features. Sure that's obvious if you give any thought to knitting, but being someone who doesn't knit it's all brand new to me. I've also learned that the knitting folks are rather pun-y when it comes to the nomenclature of the craft. Tinking is the process of un-stitching a stitch at a time and the name becomes obvious along with an instant facepalm when you realize that 'tink' is 'knit' spelled in reverse. Frogging is where you pull out several rows of stitches by yanking at the row and my inquisitive mind as to where the name 'frogging' came from it was explained, 'when you frog, you rip-it, rip-it, rip-it'........

Appropriate groans to puns aside the missus discovered that her yarn was eaten away by moths, well specifically moth larvae are the culprits. Having one's 'yarn stash' compromised is a big deal to begin with considering cost and time to accumulate the material, what was really devastating was her collection of hand-spun wool yarn from her time in Scotland which are irreplaceable. Some internet searches lead to this site where the author talks about how moth larvae can be eradicated with a temperature of around 130 Fahrenheit. The issue we've discovered that most modern ovens don't go that low (mine bottoms out at 160) and toaster oven's heating elements are far too close and damage the yarn. I start to think of how to have a controlled temp and consider a few ideas up to and including building a mini-oven with fire bricks, heating element, thermometer, and an Arduino board but settled on a far simpler idea that already exists and has all of the features already. I'm going to Sous Vide me some yarn.

First thing I need to figure out is at what temperature does yarn's mechanical bonds breakdown. Instead of empirically testing it I decided to see if someone already researched this topic and as it turns out a letter to the editor in the a 1968 edition of The Journal of the Textile Institute goes on to describe that wool's mechanical bonds breakdown starting at around 100 degrees Celsius, or 212 Fahrenheit which means that I have a pretty wide margin to play with. What I also found out that wool ignites at 228 to 230 Fahrenheit which means that I could have oven baked the wool, but what I couldn't account for with higher temps are dyes and wool filament size that may change those figures and decided to stay the Sous Vide course where there are no open flames. Another thing that I wanted to figure out is what temperature and duration would it take to kill moth larvae. A study published by Washington State University explores in detail that temps as low as 46 Celsius/114.8 Fahrenheit for fifty minutes has a one hundred percent mortality rate for moth larvae and basically states that with enough heat and time that they all die off.

With the data on hand I decide to Sous Vide the yarn at 135 Fahrenheit for one hour as the only thing that remains unanswered is if it's the temp regardless of condition, or if dry heat makes a difference. In theory, it should be way overkill, but given the varying density in spools of yarn as well as wool itself and the fact the Sous Vide is flameless where there is no concern for accidental ignition or a sudden climb in temperature breaking down wool I went with the longer cook time. The first issue I had to overcome compared to what I normally Sous Vide is just how buoyant wool is in a ziplock bag devoid of air. It took two bricks to overcome the buoyancy of three skeins of wool for those that are wondering. We pull the first bag out of its maiden soakage and inspect the yarn to discover that the first few layers had moth damage as expected. We salvage what we could of each skein and re-wrap the remainder. Overall the process worked. It was a great advantage to be able to walk away while the Sous Vide ran, running errands and such and after a day we Sous Vide her entire yarn stash. A month later and we've overserved no moth infestation and the yarn remains intact to this day since.

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