I’ve been having some fun discussions on Ravelry in an attempt to suss out some answers to the millionty questions buzzing around in my head about solar dyeing. Solar dyeing is where you let the sun do the work of your stove in the dyeing process. This is most commonly accomplished in large Mason jars, although I’ve seen solar cookers and roasting pans used, as well. The fiber and dye (or dyestuff and water) is put all together in the container. Then you let the jars sit out in the sun anywhere from a few hours to a few days, and bam!—you’ve got dyed yarn. Other steps of the dyeing process can be done with the sun, as well. The extraction process is one of these.
Right now, on my back porch, I’ve got a big jar of avocado pits stewing in a solution of ammonia and water to extract the dye. The instructions said to put this in a sunny spot and leave it for a couple weeks. So I did. And right next to this big jar of wonderfully dark red-brown liquid (the extraction is working) is my collection of unmordanted control swatches from Dye Day #1 sitting in the full sun for their lightfastness test (which mostly are failing). The other day as I was washing dishes, I looked out the window at my avocado dye and yarn swatches—I had a moment giddy squee!–and then it struck me that I was watching the sun concurrently create and destroy my dyes. How could this be possible? I’ve been thinking hard about this one for days now. My conclusion? It’s time for some science.
Here are the issues I’m pondering (please be patient as my mind wanders), and the answers I’ve got so far:
1. Some instructions for solar dyeing say not to use plastic containers, because they do not allow enough light in. This implies that it is the light rather than the heat that aids in the dyeing. But I’m pretty sure that’s not true, because if it was, dyeing wouldn’t work on the stove, in a pot. With no sun. So perhaps they meant that it’s a matter of glass doing a better job of heating up in the sun than plastic? I haven’t tested it, but maybe that is true.
2. Other instructions use dark pots or roasters to dye in, which supports the idea that only the heat matters. Which means that solar dyeing could be done perhaps more effectively in something other than a glass jar, or at least covered with black plastic to increase the solar gain.
3. It is very common for dyestuffs not to be lightfast on yarn without a mordant. Is a dye in solution equally as susceptible to photodegradation as it is on unmordanted yarn? I don’t know yet. But I think this is a pretty crucial question to answer.
4. Assuming a glass container is being used, if a fugitive dye is used in a solar dyeing process, even with mordanted yarn, does the longer uptake time (for the dye to adhere to the yarn) allow enough time for there to be detectable photodegradation of the dye in solution before it can dye the yarn? I don’t know this yet, either, but the solar dyeing that I’ve seen has suggests that the process takes a much longer time. I’ve seen experiments with one dyebath where different samples are left in for increasingly longer periods of time (up to 10 days), and the colour on the yarn just got darker and darker.
5. Which wavelengths of sunlight are most responsible for fading of dyes on yarn or in fabrics? The Florida Solar Energy Center had this to say about sunlight and fading of dyes on fabrics and furnishings, which I think is relevant:
Fading of interior furnishings is often attributed to ultraviolet radiation (UV) from the sun passing through windows onto interior surfaces. However, UV is not the only portion of the solar spectrum which can damage artwork or furnishings inside buildings. Virtually the whole spectrum is of concern, which is why long term exposure to solar radiation should be limited.
Ultraviolet radiation (UV) is the single largest contributing factor in fading of fabrics, carpets and other furnishings. Although visible light, electric lighting, heating, humidity, age of fabrics and fabric dyes all play a part in the process, UV radiation is attributed to 40% of the damage. Protecting against UV is not just important in hot, sunny climates. Even in cold, cloudy climates, UV radiation can damage furnishings.”
6. So, which wavelengths can pass through glass anyway? Apparently the answer to this can be quite variable. It depends largely on the composition of the glass. But for ordinary glass, like in a single pane window with no low-e coatings, the International Ultraviolet Association (yeah, there is one!) had this to say about it:
Normal glass (as used in windows) is transparent to UV radiation up to a wavelength of about 330 nm (or UV-A light). The transparency is quite high so almost all UV-A light will pass through glass. Below 330 nm (UV-B and UV-C), almost 100% is blocked by normal glass.“
Here’s how the spectrum breaks down according to Wikipedia (yes, i know it’s not really a reliable reference, but I think it’s safe this time):
Ultraviolet C or (UVC) range, spans a range of 100 to 280 nm; Ultraviolet B or (UVB) range spans 280 to 315 nm; Ultraviolet A or (UVA) spans 315 to 400 nm; Visible range spans 380 to 780 nm; Infrared range that spans 700 nm to 106 nm.
7. If those wavelengths pass through ordinary glass, what can pass through a typical canning jar? I don’t know for sure, but I found out that beer brewers and wine makers say that if you use a Mason jar, to keep it away from sunlight, because the UV will make a brew go bad. So, I’m going to guess that it’s probably much like regular glass, ie it lets a lot of light and UV through. Here is a great article that shows what wavelengths of light go through ordinary glass (in this case a glass bottle), and how it differs in coloured glass. I’m guessing this data would be true for canning jars.
Alright. So what do we know? Solar dyeing relies on the heat of the sun to help extract and set the dye. Canning jars are most likely totally transparent not only to the visible light spectrum, which plays at least a small part in photodegradation, but also to all UV-A light, which is largely responsible for photodegradation (and skunking your beer).
It seems logical, then, to do one of 3 things when solar dyeing:
1) Use brown glass jars (and raise a toast to our beer-brewing friends)
2) Use a dark pot or roaster
3) Use a glass canning jar, but cover it with black plastic
The point of all this? I really want to know if the sun will photodegrade dyes in solution. It could play an important part of getting clearer colours when solar dyeing, and also of getting more consistent, successful results. I think that a simple experiment would help test this. I see two ways to do this:
1) First, do a standard heated extraction of a known fugitive dye, then dye mordanted wool with half in brown glass and half in clear glass. This would test the dye in solution at the time of dyeing only. I’d do a minimum of 3 days in the sun, and I would monitor and adjust the heat of each one to rule out that variable from the equation, since some dyes change according to heat.
2) The second way would be to do a solar extraction, half in brown glass and half in clear glass. Again, monitoring the temperature. Then dye your mordanted wool with it in a standard heated way on the stove. I would use the “canning” method, where you heat water in a large pot, and place your samples in their individual jars in this bath to heat them. This would test photodegradation of the extracted solution only.
It would be interesting to see the results of this, don’t you think?
Oh, and that whole heat thing reminds me. I was talking with my husband about this the other night—he’s a scientist—and he reminded me that pH tends to change with heat, as well. Which got me thinking about a whole other issue: when a dye recipe tells you to dye at a certain pH, do they want you to check that pH in the beginning, before you heat the dyebath, or once the goal temperature has been reached? I’ve never seen anyone differentiate, but it makes a difference. Some dyestuffs, like alkanet, are quite pH sensitive. Alkanet must be used at a neutral pH. Our alkanet dyebath was acidic, so we adjusted the pH to near neutral before we heated that pot. But since pH changes with heat, and we totally forgot that little fact, we likely did not actually have a neutral dyebath once it reached a simmer. This quite possibly effected our results.
So, does it really matter when you measure pH for natural dyeing? Yeah, I think it might if you want consistent results. My husband says that in his lab, he only counts the pH that is measured at the temperature needed for the experiment. Although some dye adheres to the yarn when it’s initially dropped in, it’s typically during that hour long simmer that the bulk of the uptake happens. In the future, I will measure and adjust pH at that point rather than at room temperature, unless I’m doing a cold process dyebath.
Alright. Those are all my semi-scientifical thoughts for now. I’d love for any of you who have more experience with dyeing or science to weigh in on this. Keep the conversation flowing, keep the dyepots going!