A Trial of Hollyhock Petal Dye

These hollyhocks are Double Maroon, now blooming in my garden.  Pretty stunted, compared to the ones growing in a thin strip of dust beside a wall, only a couple of hundred yards down the road.  The books say Hollyhocks like deep, rich soil and can manage a bit of shade. Having forked out in March for six good looking rosettes, kept them in large pots in the greenhouse til the worst of the cold weather was over, then planted them out with a nice handful of cow manure each, my results do not back up the prior intelligence.  Suffice to say, I am not struggling to harvest bucketloads of petals. 
My sister Pip visited on Saturday, bringing a big bag of dried fallen hollyhock petals from her friend Claire's garden.  I put the kettle on, told my son to make the sandwiches and disappeared off to weigh out 40g and put them in a pan of cold water to soak.  Pip could tell I appreciated the gift. Apparently, these petals are from self seeded plants, enjoying the sunny South East of England and putting on a fabulous display in shades of red and pink without any special attention.

First thing Sunday, I brought the pan up to a simmer for half an hour.  Once it had cooled, I put in 40g of wool, mordanted with Alum and Cream of Tartar and left it to soak.  The books I have both say that different coloured flowers give different coloured dyes, but one author said there would be yellows and browns on wool with this mordant, the other showed a spectrum of purples. Hooking the wool up for inspection after a cold dip in the deep red bath, it looked to be turning greeny yellow. Interesting, though it doesn't show so well in the photo. Time to give it a little simmer.
While the rain poured down, I did an internet search on hollyhock dye.  A couple of blogs showed a sophisticated, pale, turquoise blue, others, shades of grey and mauve.  This paper from India studies ultrasound as a method of getting hollyhock dye into wool and cotton, rather than using heat.  The authors discuss the chemistry of chelation, fixing various dye molecules onto the mordants.  I infer from their work that firstly, strong chemical binding leads to the good wash and light fastness they discovered, and secondly, that all hollyhocks are likely to contain several different pigments, not just a single one, like indigotin in woad.  

The Indian study used deep pink flowers and described bright green results on wool using the same mordants as me.  Sure enough, I found my wool had gone green after heating.  I put another 40g skein into the afterbath, simmered it up and left it to soak overnight.  I got a paler, but tonally similar green (better than the photo suggests) and decided that was the best of the bath used up.

That same afternoon, when the rain stopped for a bit, I went out to look at my own Double Maroons.  Ten flowers had actually curled up and fallen to the path and two more were loose enough to be fair game. All were still quite fresh, so they just got simmered straightaway.  Although much larger than the dried ones, and a frilly double petalled variety,  twelve flowers didn't seem much, so I only put in a test skein of 12g alum and cream of Tartar mordanted wool.  

The dye bath was another deep magenta red, but this time, the wool came out blue.  A series of 12g skeins have been simmered and soaked over the past few days.  The first skein, far left, had a greenish cast not present in the second skein, leading me to guess that the yellow pigments might get fixed on to the mordant most easily and thus cleared from the dyebath first.  The cold soak in the dried flower dye bath made the wool yellow, before heating moved its colour to a good green, presumably due to taking up a blue pigment.  When the third 12g skein came out with a mauvish blue, I thought I might get an increasingly red series, trending to purple, but the next two were a simpler blue in successively paler shades.  The final skein has a greyish lavender cast. These colours are excitingly complex.  

Finally, I had to see what changing the pH would do.  One end of each skein was put in water with vinegar and the other end in a solution with soda ash. Alkali turned the blue into green and the green into brown (centre of photo).  Acid provided the final flourish - purple and lime green.  I should get the alkali result from washing anything I make with these skeins in washing powder, which is generally alkaline.

Hollyhocks are like a familiar, kindly Great Aunt, much loved by later generations who would never suspect she had run a farm, brought up a family and taken in an evacuee, pretty much singlehandedly during the war, simultaneously saving the life of her premature son by keeping him constantly in a homemade papoose. Private strengths and deep qualities to fathom beneath a cottage garden appearance. Next year, I'll plant some more in the sun by the new wall.