Posted by Helen
I am writing this article on mordanting firstly and mostly for my own benefit and secondly because while there is some really good stuff out on the internet I have also read a lot of nonsense talked too as it is a subject that seems to attract some cock-eyed ideas. For example all mordants are sometimes clumped together as being equally toxic, whereas they vary widely in toxicity, and the converse view is sometimes held that all mordants are equally safe to use. I use quite low levels of mordants as most modern dyers do but on discussing the environmental impact of high levels of mordants and of some mordants in particular I have been told – “why bother! How many people look at the contents of their cleaners under the sink and many of these are much worse than mordants”. J N Liles, who was a retired Chemistry Professor, wrote a definitive book on Natural Dyeing “the Art and Craft of Natural Dyeing, Traditional Recipes for Modern Use”, he said that mordants are mostly no more dangerous than the majority of chemicals stored around the house but also that both groups should be treated with respect. However I do read the list of contents on my cleaning materials and am careful to use environmentally friendly cleaning products so I also want to be as careful as I can be to use as little of mordants as I need to achieve the effect I want.
I have also been told that as a “craft dyer” it does not really matter what I do as I don't dye enough to have any impact on the environment However I am a great believer in the slogan “think globally act locally”. The only person whose effect on the environment I can really do something about is me so I do what I can.
However experienced as natural dyer I think that mordanting is a subject that is worth revisiting every now and again as it is a very complex subject with a huge range of different techniques.
Nobody really knows when people first started to use mordants, although it would seem that the first mordants were probably the iron mordants in the form of ferruginous mud or mud with a high level of iron. Dominique Cardon in Natural Dyes suggests that it would have been fairly obvious to prehistoric people that iron rich muds caused a change in colour as tannin bearing leaves drifting down into it would have gone black. That as may be the evidence is that mordanting with iron was known as early as the time of Tutmos 1V of Egypt 1542 BC-1305BC and that the Egyptian dyers knew enough to get a range of colours from light brown to black. (Dominique Cardon)
What is a mordant?
The simplest way of describing a mordant is a chemical that bonds to both fibre and dyes and acts as a sort of bridge between the two. However the complex almond shaped lattice structure formed by calcium ions,madder and alum, show that in this case at least it can be more complicated. (Dominque Cardon) India Flint in her book Eco Colour turns the view of Chrome (Potassium Dichromate) as a mordant on its head suggesting that plants acids fix the so called mordant to the fibres rather than the other way round.
The following is a list of all the chemicals I have seen mentioned as mordants. Heading the list is Alum ,Potassium aluminium sulphate, ammonium alum ( sometime known as pickling alum) then the other more usually known ones mentioned in many if not all dye books; Ferrous sulphate, Copper sulphate, Stannous Chloride, Potassium Dichromate (which I don't use -more soon). Slightly more unusual, although becoming more common, is Aluminium Acetate - principally as a mordant for cellulose fibres. Other mordants include iron acetate ( eported to be less corrosive than ferrous sulphate), pewter (dissolved in Nitric acid) tannic acid, citric acid, oxalic acid, vinegar as an impure form of acetic acid, acetic acid, wood ash lye (potassium hydroxide & potassium carbonate ), urine as ammonia, ammonia, bismuth, sodium chloride or salt Murio sulphate of tin (muratic acid being an old name for hydrochloric acid) [Bancroft's mordant ]). Bancroft noted for example that tin dissolved in either pure citric acid or lemon juice gave the best scarlet with cochineal (Gerber-Cochineal and the Insect Dyes) and also that it was not the metal mordants alone that defined the colour of cochineal but the metal mordants with acids. John Edmonds in Medieval Textile Dyeing includes “saltpetre” or potassium nitrate, as a mordant mentioned in Rosetti's Plichto and which used to create a green dye with vinegar, sal ammoniac or ammonium chloride, and “ a little common lye” which was probably stale urine and thus ammonia. I also mention with a certain amount of hesitation because they are so poisonous the mordants used in many 16th & 17th century recipes but the use of which John Edmond (The History and Practice of 18th Century Dyeing) said was dying out by the 18th century. These were derived from arsenic,and were arsenic trisulphide (orpiment), arsenic monusulphide (realgar) Arsenic bisulphide (red orpiment) . Almost any soluble metal salts can be used as a mordant.
Then there are the chemicals used to fix madder onto cotton for Turkey Red such as animal dung , and castor oil to name just a few
Finally there are plant sources for mordants, such as the tannin bearing plants, sumach, oak galls, cutch, pomegranate rinds, the alum accumulators defined as plants that collect 1000mgkg-1 alum (=0.1%) in dry leaf matter) Dominque Cardon). Most of these 1600 or so plants are tropical or semi tropical plants, the northern European plants are the club mosses, now unfortunately rare but used by the Vikings in York for example and in Scotland in particular up until the 18th century at least. (Su Grierson Colour Cauldron) Gerber points out that native South American Indians immersed cochineal dyed fabrics in iron rich muds to create purple and many peoples use iron rich muds with tannins to create black on fibres and fabrics as well on reeds for baskets.
While we know mordants were used and known there is very little precise information written down till Rosetti published his Plichto in the Art of Dyers (collection of dye recipes) in 1548) Even then Rosetti was not himself a dyer but recording details of the dyers crafts. However from then on more recipes were published and as the knowledge of chemistry improved the mordant recipes and dyeing process of the commercial dyers became increasingly complicated. Partridge's Practical treatise on Dying (sic) published in New York in 1823 described how a commercial dyer could reproduce 2000 colours using some 30 dye stuffs and 15 mordants. This is contrast to modern dyers who use more plants-John Edmund says up to 140- and less mordants,12 (including Chrome) which William Partridge would not have known about. The recipes seem to have become simpler since the heyday of commercial dyeing whether this is because of loss of knowledge (William Morris is reported to have found it difficult to find experienced natural dyers some 20 years after the introduction of synthetic dyes-although I can't track down the reference for this) or because the craft of natural dyeing was largely kept alive in the 20th by craft dyers rather than large scale commercial dyers. However significant information seems to have been lost, for example many modern dye books use a standard recipe for mordanting wool with alum whereas Partridge writing of the dye books written by Bancroft and Cooper points out they had missed some of the essential minutiae and says that mordant recipes should vary for different colours. “they prescribe a given quantity of mordant in proportion to the weight of the goods dyed, without reference to the colour,or state of the goods. There are but two colours that will admit of the proportion prescribed by them being used, which are red and yellow-were one forth or one-fifth of alum used in general,it would ruin the colours, and if that portion were used on wool ,it would never be wrought onto cloth) - .Apparently also forgotten was the need to oxidise and air fibres or indeed to allow the dye baths themselves to oxidise a process which is being rediscovered by the new modern dyers dyeing for a living such as Debbie Bamford of the Mulberry Dyers as well as by the Japanese scientist Seiju Yamazakis who found allowing dye bath to oxidise for one to two days is an important part achieving good even colours. (Dominque Cardon) In past times mordanting was sometime repeated up to 30 times for example as in creating violets in Japan (Dominique Cardon) or fibres were put from the dye bath to mordant pot and back again sometimes many times to increase depth of colour. While we have cause to be grateful to the crafts dyers who kept natural dyeing knowledge alive I think we ought also be concerned how information is simply repeated across dye books as a given. Perhaps it time to re-examine some of our techniques.
I am starting off with alum as a mordant as it is the one most often used but I am planning to write about many of the other common mordants.
The History of the use of alum.
Dominique Cardon has a lot about the history of alum which I have read but the source for a lot of information comes originally from a monograph “ about alum The Earliest Chemical Industry” by C Singer published in London. This book is obviously a collectors item as it sells for about £180.00 so I have not been able read it. However I own an enormous debt to Dominique Cardon as most of the information on the history of alum and how it is produced come from her book “Natural Dyes”.
I am starting off with the history of alum as I was fascinated to discover for how long it is use has been known and also how widespread its use has been. It would seem that wherever people dyed they knew about alum. I am no archaeologist so could well find I am wrong but I understand that if a technique is widely known as for example spindle spinning or indigo dyeing is then it means that the knowledge of it of is rooted in very ancient history indeed.
Alum is the most important derivative of aluminium. Aluminium in fact was named after alum, and is one of the most common metals 8.3% by weight, iron being the next with 6.2% Alum itself as a mordant has been known for 1000's of years as both hieroglyphics and cuneiform contain words for alum.
The oldest form of alum is the hydrated double sulphate of potassium and aluminium (AlK(SO)4)212H2O and is found in deserts and in volcanic areas close to fumeroles (vents for volcanic vapour) and the best known sites in antiquity were the oases of western Egypt, volcanic island of Melos , the Aeolian archipelago and volcanic areas of Sicily and southern Italy. The earliest evidence for it's use comes from Mesopotamian civilisations where there is not only a word for alum in cuneiform but also another for alunite from which alum is derived, suggesting they knew how to process alum. Egyptian heiroglyphic also has word for alum and alunite. Further documentary evidence for it use is a famous set of documents known as the Leiden and Stockholm papyri and which date from the end of the 3rd century/beginning of the 4th AD. However the content is based on earlier literature mainly the work of Bolus sometimes known as pseudo Democritus who lived in Mende in the Nile Delta between 200 and 100 BC, and the recipes are for imitation purple where the mordant described is Phrygian Stone which was probably made from alunite, a source of alum. Documentary evidence shows that alum was known and used in China from AD 618-907 as the tax on it is mentioned in the Imperial Budget and it was known in Japan by the 8th C. Despite the expertise of the Indian dyers there is no documentary evidence of its use in India till 13th Century. The native South Americans certainly knew and used alum as a Jesuit Priest Bernabe Cobo recorded 4 or 5 types of alum rock being known and used by the Peruvians when he arrived in 1598 and similarly friars arriving in Mexico in 1524 found various types of alum in use.
The ancients had also discovered how to separate Potash alum (Kal3(SO4)2(OH)6) from alunite or alum stone which contains all the elements of potash alum but also alumina (Al2O3). They calcined the stones (heated them ) to 700 degrees C , then poured water on the result until the a paste was formed before lixiviation or boiling of the paste , this causes the alunite to break up and turns into soluble alum and alumina. The “mother liquor” is poured off and allowed to crystallise. This is very pure potash alum but the yield from the stone was quite low. In 1543 the fall of Byzantium to the Turks cut off the supply of alunite to western civilisations but an intense search resulted in the find of a site near Rome which supplied Rome alum for 4 centuries.
The next stage in the production of alum was the discovery of how to produce alum from pyritic shales . There was a famous site near Whitby in Yorkshire , the process was quite complicated but involved the use of stale urine (the only source of ammonia) bought to Newcastle from London and the origin I believe of the phrase “taking the piss”. This process was also known in China by 1596.
From the 1850's sulphuric acid was used to produce alum from the pyrite shale and finally the Americans started to create a pure aluminium sulphate by using sulphuric acid and kaolin (china clay).
I have talked about the history of alum and how widespread the use of it was throughout almost the entire world so the use of it by a modern dyer is put into perspective and also because I like the sense of being linked to dyers spread through time and space.
Safety of Alum
This site maintained by the Department of Physical Chemistry at Oxford University and it says that alum is defined as not toxic according to EEC directive Directive 67/548/EEC.
To use alum safely Do not inhale dust, avoid contact with skin and with eyes.
Alum is the most common of mordants, mentioned every where in all dye books
I have heard people refusing to use alum as it a metal salt (so is ordinary salt- sodium chloride) , because it is aluminium based and because they want a zero risk process. So what is alum and how dangerous is it to use?
Potassium aluminium sulphate or alum (AlK(SO)4)212H2O]
Michelle Wipplinger on her Earthues Site www.earthues.com points out that true "alums" by historical definition are double salts of aluminium such as potassium aluminium sulphate. However aluminium sulphate has also come to be known as "alum". The difference is subtle she says but may affect your dye results. Aluminum sulphate is the result of the refining process of bauxite which is the raw state of aluminum ore. During this refining process sulphuric acid is used to remove most of the iron and silica present in bauxite. Further purification with potassium yields an aluminium sulphate with fewer impurities, especially iron which could dull the colour on the fibre. If in doubt she suggests that you try a sample first.
There is no zero risk in natural dyeing, in my opinion, and I think that it is absurd to feel that there might be. There does seem to be an implied assumption sometimes that natural dyeing is eco friendly, green and safe. However this is only true if the way natural dyeing is done is in an environmentally responsible way and let us not forget that medieval dyers contaminated rivers and that plants can be poisonous too. In terms of poisons most of us dyers point to rhubarb leaf which produces oxalic acid which is poisonous as a reminder that it need not be safe. If you really want very safe dyeing have a look at the delightful chapter in India Flints Eco Colour which tells you how to make coloured icing from plants that is safe to eat.
I agree with Liles who says that preparation is essential for good dyeing and while this post is all about mordanting it does assume that you have clean scoured fibres free from oils, grease or naturally occurring oils and that fibres & fabrics are well wetted out.
How to keep yourself safe.
Health and Safety
Protect yourself with gloves, face masks and aprons as appropriate
Never use anything for dyeing that you will later want for cooking
Do not eat and drink ( or smoke) when using dyes or mordants.
Dispose of used dye baths responsibly.
Keep dyes and mordants away from children and pets
As Liles points out instructions for the disposal of the mordant and dye baths is not an easy one to lay down the law about as they differ in toxicity and acidity etc. In the case of alum he recommends that spent alum bath can be disposed of down the drain unless it is into septic tank, with plenty of water . You can also dispose of it around any acid loving plants such as azaleas.
JN Liles also recommends as a general principle that you don't boil mordant baths as a solution of a metallic salt such as chrome, tin, copper alum and iron do not enter the air unless the solution boils. When boiling the dissolved salt does enter the air in a small amounts of fine water droplets, a precess called entrapment. A few years ago I mentioned this in a debate on mordants and was shot down in flames, told I was talking nonsense and that it did not happen. At the time I could not find the reference so I was pleased to come across it again on p 13 of Liles book. Even though it is a minor point it goes to show how careful you have to be when following information provided on the internet especially when no authority or source is given for a statement.
Dye books most usually describe mordanting as pre mordanting, dyeing in a one pot method, and post mordanting and colour modification and tell you to heat over an hour, simmer for an hour and allow to cool but once you understand the principal of mordanting you can play around with temperature and time. For example you can slow the process down, mordant at low temperatures but take longer and indeed cold mordant over a long period of time
Traditionally natural dyers were told by dye books to use alum at a ratio 25% of dry weight of fibres This means that if you have 100g of fibres (weighed dry) you would weigh out 25g alum and you will find these levels in old dye book up to about the 1980's. Gerber says that this quantity was based on an untested assumption that the more mordant you used the more colour would be fixed to the fibres. 25% was the top limit as any more made the wool feel sticky. It is a classic example I think of how processes simply got copied from one dye book to the next. However in 1985 a book that has never been bettered, in my opinion, on the subject of mordanting was written by Gill Dalby called Natural Dyes Fast or Fugitive, published by Ashill publications ISNB 0 948020 00 8.and is a book that all natural dyers should have on their shelf. The reason for this is because not only did Gill Dalby look at the light and wash fastness of many natural dyes she also looked at mordanting quantities and processes and produced recipes which use very much less of not only alum but also all the other common mordants. Gill Dalby describes how to improve the take up of mordants by the use of an assistant. In the case of alum this is cream of tartar and the addition of cream of tartar to the mordant bath improves the take up of alum by the wool. The use of cream of tartar has been known for centuries of course but she also found that you could use much less alum than had been used in current dye books. Cream of tartar is the common name for potassium hydrogentartartrate (KO2CCH(OH)CH9)H)CO2H mixed with calcium tartrate This forms on the inside of wine casks but now you can buy in the supermarket as cream of tartar.
Mordanting wool with Alum
This Gill Dalby's pre-mordanting recipe for wool which I still use.
To premordant wool
8% aluminium Potassium Sulphate
7% cream of tartar
Dissolve the alum and cream of tarter in a small amount of warm water and stir until dissolved. Put this into a mordant pan top up with water add the fibres and bring to the oil over an hour, simmer for an hour allow to cool. Rinse to remove unfixed mordant, spin off excess water and store damp until wanted.
Various other well known authors use slightly different quantities. Trudy Von Stralen in Indigo Madder and Marigold uses 10% alum, 5% cream of tartar and Domnique Cardon says to use 15% alum and 6% cream of tartar for mordanting wool. John and Margaret Cannon in Dye Plants and Dyeing use 18% and 6%. However they also say to use formic acid as an assistant to alum at 8% citing Gill Dalby as the source. Now formic acid is the assistant Gill Dalby recommends for use with Potassium Dichromate as it significantly improves the take up so this reference is a bit bewildering.
There are variations to this. If you are dyeing cochineal mordanting with cream of tartar fixes more colour onto the fibres, but if dyeing with madder the cream of tartar will move the colours more towards the orange, this is because the cream of tartar makes the mordanted fibres weakly acid. However if you rinse the fibres carefully the acidity is said to be removed and it is then okay to dye with madder. However if dyeing without cream of tartar use with alum on its own using 12% alum to dry weight of fibres. (Dominique Cardon) Partridge in his Practical treatise on Dying gives a recipe for mordanting for madder using 60-70% dry weight of madder to fibres, he recommends the use of 6-8% aluminium sulphate and 5-7% cream of tartar
Cold Mordanting of wool.
I first came across this as a Turkish Rug weavers method .
Dissolve 35% dry weight alum to fibres .
Make up the mordant to a litre of solution for 100g of fibres.
Pour over the dry fibres, working the liquid. Into the fibres. If there is not sufficient add more liquid.
Leave, turning every day in the liquid for 28 days.
Mordanting silk with alum.
You can of course mordant silk the same way you do wool but keeping the temperature down to 180°F , 80° C but you can also cold mordant silk. This recipe is -again- from Dominque Cardon and since I discovered it just in time to use it Biannual Association Summer School of Weavers Spinner and Dyers 2007, I have used it a lot.
Cold mordanting of silk.
Weigh out either 35% dry weight of fibres alum or
30% dry weigh of fibres and 15% cream of tarter.
Dissolve in hot water, add to a bucket of luke warm water and then remembering to wear gloves immerse the silk in the water, work with your hands for a few minute and leave overnight.
I have two questions about this that I have not yet answered. One is how much of the mordant does the silk take up? And a related question how much is left and could this then be used for hot mordanting of wool?
Mordanting of cellulose Fibres.
I always use Alumiunum Acetate for this and no longer use the longer alum/tannin process.
The easiest mordant to use for cotton & linen is aluminium acetate, This replaces the more traditional method which involves at least two days of mordanting to get good colours. The drawback is that is only available from a few specialist suppliers but it is so quick and effective that it is worth getting.
Use 5% aluminium acetate for dry weight of fibres (WOF). If you don't have scales I suggest that you use 1 level tsp of aluminium acetate to 150g of cotton.
Health and Safety
Aluminium acetate is a very fine powder. When weighing it out wear a dust mask (available from hardware stores) and gloves.
Dissolve the aluminium acetate in very hot water and add to the prepared bath.
Stir with a stirring stick and enter your fibres, bring to the simmer and simmer for one hour
Allow to cool, rinse.
Spin to extract the excess moisture, and store damp till wanted. I keep my mordanted damp fibres and fabric for months in box with a lid.
A different approach to mordanting and Dyeing
Dominique Cardon reports on the Japanese technique developed at the beginning of the last century when Japanese scientists put natural dyeing onto a scientific footing. This is not method I have yet tried although it is on my list to experiment with. Here dye baths were made with multiple extractions- which is something I now do leaving most of dye bath for one or two days to oxidise. Fibres are dyed in the dye bath with silk being boiled for 15 minutes and cotton for 20 minutes, while wool heated at 80 °C for 30 minutes, and allowed to cool before being immersed in a lukewarm mordant bath of either 5% aluminium acetate. 1% iron acetate, or 3% copper acetate or wood ash lye from plant accumulators of alum. The fibres are left in the mordant bath for 30 minutes adjusting the concentration to achieve a pH of 10inhte case of woodash lye bath. The fibres are now dyed again. In case of silk, this is added just to the bath before the dye bath is boiled and then left to cool Wool is heated to boiling point in the dye bath, the wool is acidulated to pH 6 and allowed to cool in the bath. Cotton on the other hand is boiled in an alkaline dye bath at pH 8 for 20minutes and then allowed to cool for at least 12 hours . All fibres are then rinsed and dried in the sun.
Copyright Helen Melvin 22nd January 2009.
You are welcome to use this information for personal use but it is not be used for commercial gain
John and Margaret Cannon Dye Plants and Dyeing Published by the Herbert Press Limited
Elijah Bemiss The Dyers Companion (1806) Published in 1973 Dover Publications ISBN 0-486-20601-7
Dominique Cardon Natural Dyes Sources, Tradition Technology and Science Published by Archetype Publications !SBN 978-1-904982-00-5
Gill Dalby Natural Dyes Fast or Fugitive Ashill Publications ISBN 0 948020 00 8
Frederick H. Gerber Cochineal and the Insect Dyes Published by the author ISBN 09601814-3-
John Edmonds MedievalTextile Dyeing Published by the Author ISBN 09534133 22
John Edmonds The History and Practice of Eighteenth Century Dyeing published by the Author 1SBN 0 95341340 3
Sue Grierson The Colour Cauldron Published by the author ISBN 0 9510132 11
J.N.Liles The Art and Craft of Natural Dyeing Traditional Recipes for Modern Use Published by University of Tennessee Press 1SBN 0-87049-670-0
William Partridge A Practical Treatise on Dying Originally published in New York in 1923 by H Walker and Co. Pasold Research Fund Ltd
G. Rosetti 1648 The Plichto of Instructions in the Art of Dyers ( 1969 Translation of the first edition of 1548 by Edelstein and Borghetty. Cambridge M.I.T press.
Trudy Von Stralen Indigo Madder and Marigold published by Interweave Press ISBN 0-934026-86-6