alum quantity for fabric marbling

In recent posts I’ve looked into the types of alum and the quantity necessary for marbling paper; now let’s turn to fabric marbling. There are a lot of different recipes for mordanting fabric prior to marbling, but with my natural dyeing experience to guide me, I’d like to share my method.

alum quantity for fabric marbling

Remember that alum is the compound most commonly used to mordant both fabric and paper. It bonds readily and permanently to other molecules, creating a link between fiber and marbling pigment. Our aim in mordanting is to evenly apply an alum solution to our fabric before marbling, just enough for a permanent print.

Fiber preparation

Firstly, choose an absorbent natural fiber or blend for your fabric. Thoroughly wash the fabric to remove any starch, sizing, or dirt from its surface - these will impede both the mordant and marbling from being absorbed.

Mordanting by weight

Using a metric baker’s scale, weigh your dry fabric (this can be done before washing).

  • For plant fibers (cotton, linen, bamboo, ramie, hemp) or fiber blends, measure alum equal to 15% of the weight of your dry fabric.

  • For animal fibers (silk), measure alum equal to 8% of the weight of your dry fabric.

Fill a clean container with enough warm water for your fabric to swim freely. This can be a bucket, plastic storage container, or your bathtub. Add the alum to the water, stirring until it is completely dissolved. Lower your fabric into the alum solution, swishing it around to release air bubbles. Leave the fabric to soak for 40-60 minutes, stirring every 15 minutes for even absorption.

Empty your mordanting container and fill with fresh water. Rinse your fabric 1-2 times by wafting it through the water to remove excess alum.

Hang the fabric to dry. Mordanted fabric may be stored for up to 6 months before use. Iron with steam before marbling.

Mordanting by volume

If you don’t have a baker’s scale, you may choose to mordant by volume instead of weight. It’s not quite as scientific for large amounts of fabric, but it works well for small projects.

Find a container large enough for your fabric to be fully submerged and swim freely when it is unfurled. Fill this with warm water, measuring as you go. For every quart of water, add 1 1/2 teaspoons of alum (that’s 2 tablespoons/gallon). Stir until the alum is completely dissolved, then lower your fabric into the alum solution. Swish it around to release air bubbles and leave the fabric to soak for 20 minutes.

Empty your mordanting container and fill with fresh water. Rinse your fabric 1-2 times by wafting it through the water to remove excess alum that is not bonded to the fabric.

Hang the fabric to dry. Mordanted fabric may be stored for up to 6 months before use. Iron with steam before marbling.

The dangers of poor mordanting

I’ve seen recipes calling for as much as 1 1/4 cups alum (20 tablespoons) per gallon of water. That’s a lot. The problem with mixing a very strong mordant solution by following a heavy-handed recipe or failing to follow any recipe whatsoever may not be immediately evident. But some problems might arise:

  • Alum is slightly acidic. You can over-mordant your fabric by mixing a very strong alum solution or leaving the fabric to soak too long. Over time, that acidity causes the fibers to become brittle and break apart. If your marbled fabrics feel very dry or brittle, or if they tear during washing or sewing, they are likely over-mordanted.

  • I’ve read that alum ‘eats’ or ‘decomposes’ fabric, and it should never be mordanted more than a few days prior to marbling. This is true only if you over-mordant and thus leave your fabric in an acidic state. Following a decent recipe will allow you to mordant fabric months in advance of marbling with no detriment.

  • Failing to rinse your fabric after mordanting can leave it with excess alum sitting on the surface that is not bonded to the fibers. If the un-rinsed fabric dries with any wrinkles, that alum can pool in the creases and give you a streaky print.

  • Fabrics that have not been rinsed can deposit excess alum into the size, degrading it over the course of multiple prints. Or worse, your print may bond to the layer of alum sitting on the surface of the fabric, then flake off during rinsing.

Unfortunately fabric that is over-mordanted cannot be saved; alum forms permanent bonds and cannot be removed. If you have a batch of fabric exhibiting any of the issues above, best scrap it and start fresh. Small amounts of mordanted natural fiber fabrics (not yet printed) can be torn into thin strips and added to the compost.


Further Reading

overmarbling

An overmarble or double marble is created by printing over the top of one marbled design with a second print, allowing the two to commingle. These can be very beautiful and subtle designs, often relying on a lot of negative space or transparency in the second pattern for the first to peek through. Overmarbling can be risky- the second design can save a shabby print, or ruin an excellent print. Below is a lovely example by Don Guyot held by the University of Washington Libraries Special Collections, showing the first pattern alone and with the second laid over top:

Don Guyot double marble, University of Washington Libraries, Special Collections

Don Guyot double marble, University of Washington Libraries, Special Collections

I’ve read that overmarbling requires a second mordanting between the first and second prints, but I’ve have mixed results when overmarbling fabric. Continuing with my experiments into alum and alum quantity, I decided to test the assertion that a second mordanting is required for a double print.

Process

Using 1.5 teaspoons alum per pint warm water, I pre-mordanted paper and pressed it between blotting papers for 1 hour. After the first print with watercolor paints, the paper was rinsed, dried, and pressed again. Sample A was printed with a second design immediately, and Sample B was given a secondary mordanting and pressing before printing again.

overmarble with watercolor paints

overmarble with watercolor paints

  • A Preliminary mordanting only

  • B Preliminary mordanting & secondary mordanting prior to second print

As you can see, Sample B was able to absorb and retain much more of the second print than Sample A. While both are reasonably attractive designs, it is much preferable to have the control offered by a second mordanting in order to strategize the transparency and negative space in the second design.

It seems that, because alum readily bonds permanently with other compounds, it fixes a thin layer of paint and size to the paper with the first print. Gentle washing rinses off the excess, but even in areas of negative space a film of carrageenan remains bonded to the alum. This will hinder the second print from bonding, leaving only a faint image.

My recommendation: After the first print, gently rinse, dry, re-mordant, and press before each subsequent print. Follow a recipe when mixing your mordant solution to avoid overly acidifying your paper. I’ve made overmarbled designs four prints deep with this technique. With each re-wetting the paper is more likely to become damaged, cockled, or generally misbehave, so apply mordant and take prints very carefully.

Overmarbling Fabric

Double prints or double sided prints can be made on fabric in the same way. A double sided print on a light, diaphanous fabric has the lovely appearance of a double marble. Sometimes the second print will transfer beautifully without re-mordanting, particularly if it’s printed on the reverse of the fabric, which did not come into direct contact with the size. But to avoid the frustration of a sadly pale print, I recommend re-mordanting between prints on fabric as well as paper.

Remember, wet fabric cannot absorb a marbled print, it must be thoroughly dried and ironed between prints.

double sided silk scarf

double sided silk scarf

Note: Suminagashi

If you are creating suminagashi designs on washi, mordanting is not needed for the first or any subsequent prints! Washi is so absorbent it doesn’t require alum to fix the pattern. However, suminagashi on fabric does require the same mordanting steps as above.

alum & lake pigments

In the last post, we discussed the quantity of alum necessary to marble with watercolor and acrylic pigments on paper. There is another class of pigments that can be used for marbling, and was historically an important source of particular hues. These are lake pigments, made from natural dyes. As both a marbler and a natural dyer myself, these pigments are of great interest.

What are lake pigments?

Natural dyes (with the exception of vat dyes including indigo) are water soluble. This means they cannot be used for marbling, as they simply dissolve into the size. In order to make these beautiful organic colors, many of which have no counterpart among mineral colors, useful for  marbling they must be converted into pigments. A lake pigment is made when dissolved dye is precipitated onto an inert substrate - often potash alum. The precipitate is then filtered, washed, and ground. For marbling it can be mixed or mulled with a binder, usually watercolor medium, and used like any other watercolor paint.

If you've ever used the all-in-one dyeing method of mixing mordant, dye, and fiber in one pot, you may have noticed some of the dye spontaneously settling to the bottom. This means the dye and alum have bonded together, making a lake pigment.

mulling watercolor

What role does alum play in lake pigments?

As we learned about alum, it readily bonds to dye molecules, making it a substrate well suited to the formation of lake pigments. Other mineral mordants can function the same way, such as tin and copper salts. Each of these mordant substrates acts to stabilize the dye compound, improving its lightfastness. And just as with natural dyes applied to fabric, the choice of mordant and pH can strongly affect the shade of a lake pigment.

The example below is a lightfastness test of homemade lake pigments( yes, I need to practice patience in grinding pigments). On top is madder lake with copper; below it is weld lake with a little indigo, mixed as watercolors. The left side was exposed to direct southerly sunlight for one month, and the results I think are quite promising. Unfortunately lake pigments suffer from a bad reputation because they are not as permanent as their modern synthetic replacements or mineral pigments. Some lake pigments are certainly fugitive, and care should be taken to keep artwork made with them out of direct sunlight. The most lightfast pigments are made from the most lightfast dyes, such as madder, buckthorn, and weld.

Lightfastness test of madder lake and weld lake. Left side exposed to sunlight for one month

Lightfastness test of madder lake and weld lake. Left side exposed to sunlight for one month

Marbling with lake pigments

Because lake pigments contain a mordant within them, paper does not need to be pre-mordanted before marbling! I have read this in multiple sources, and the test below confirms it.

  • A: Unmordanted paper

  • B: Paper pre-mordanted with 1.5 teaspoons alum/pint water

The mordanted paper absorbs the marbled print a bit more quickly with a slightly sharper quality, but this shows that pre-mordanted paper is not a requirement.

Lakes are prepared for marbling just like any other watercolor pigment: each color is thinned to a good consistency and mixed with the appropriate amount of surfactant. You don't need to go through the trouble of grinding your own pigments to enjoy working with lakes, any 'genuine' watercolor lake such as rose madder or carmine will work. It can be difficult to know just what manufacturers put in their paints, and whether they are synthetic pigments simply bearing the names of historical shades, so it's worth seeking high quality paints if you want the real thing.

If you are marbling with a mixture of genuine lakes and pigments from other/unknown sources, pre-mordanting the paper is advisable.

testing alum mordant with lake pigments

In addition to lake pigments, I've read that any genuine earth pigment may be used for marbling without a mordant, as earth pigments are composed of minerals. It is clear from natural dyeing that ferrous salts are a very effective mordant, so the iron present in earth pigments should work the same way. I hope to test this in future, and make a comparison of the lightfastness of these samples.

Update: After 1 month of exposure to direct sunlight, no fading has been observed in samples printed on mordanted and unmordanted paper. The alum and chalk present within the lake pigments appears to stabilize the dye colorants admirably.

Please feel free to contact me with any insights or sources for historical pigments!


alum quantity

When preparing paper for marbling, it is pre-mordanted with an alum solution. We discussed the role and varieties of alum in the last post, and let's continue with the question:

How much alum to use?

Marbling instructions vary greatly in the strength of the alum solution recommended to mordant paper. I've seen measurements ranging from 1.5 teaspoons to 5 tablespoons per pint of water. Let's investigate just how much is enough to make a successful print.

What can go wrong?

If too little alum is used, marbled designs made with watercolor or acrylic pigments cannot bond to the paper. Western-style papers used in the European marbling tradition are sized to improve their durability and slow their absorbency. Alum bonded to the surface of mordanted paper is the chemical helping hand essential for linking marbling pigments to the paper fiber, and stabilizing the colors for lightfastness in the long term. Any marbler who has accidentally printed on the unmordanted back side of a sheet is familiar with the disappointment of watching their design wash down the drain with the rinse water, having no alum to hold it fast.

However, if too much alum is used, crystals may build up on the surface of the paper without actually adhering to to the paper fibers. In this case a bit of the excess alum will dissolve into the size as each print is made. If the size becomes polluted with alum, it causes the paint to clump together in a very frustrating way, and must be replaced with fresh size.* If you can feel a buildup of powder on the surface of your paper or see white streaks on colored papers, you are using too much alum.

Additionally, alum is acidic, and using a lot will both waste alum and make the paper overly acidic. Over time, this causes the paper fibers to become brittle and crack apart.

Watercolor Pigments

Watercolor Pigments

Testing Alum Quantity

These samples, excepting sample A, were coated with a wash of aluminum sulfate dissolved in warm water:

  • A no mordant

  • B 1.5 teaspoons/pint

  • C 1 tablespoon/pint

  • D 2 tablespoons/pint

  • E 3 tablespoons/pint

As can be seen in both the watercolor and acrylic tests, unmordanted sample A is comparatively very pale. This was not a surprise, as it has no mordant at all. I was surprised, however, to find no discernible difference the in strength of the colors in samples  B-E. Any quantity of alum from 1.5t - 3T per pint acts as a successful mordant.

Acrylic Pigments

Acrylic Pigments

My recommendation: 1.5 teaspoons alum per pint water

I will continue using 1.5t/pint to mordant papers in future, the amount recommended in the first marbling class I took with Stephen Pittelkow. As alum is slightly acidic, I prefer to put as little as needed on my paper to get the job done. Pre-nineteenth century marblers used potash alum, but nowadays you can mordant with either potassium aluminum sulfate or aluminum sulfate - just mix it with warm tap water to ensure the crystals are fully dissolved. Some marblers soak their paper in a mordant bath, some apply the alum solution with a natural sponge or a spray bottle; I use a wide foam brush. As each sheet is coated I flip it over and pencil an X on the back. The whole stack of wet papers is weighted with a heavy board to stay flat. They can be printed in about half an hour when still slightly damp, or kept up to 4 days. I prefer to print papers within one day of mordanting.

If you've prepared your papers with mordant but the marbled design doesn't adhere, you may be using archival paper coated with calcium. Choose a different paper stock and try again.

*Of course, any mistake can become an interesting pattern when repeated intentionally! Mixing a little bit of alum into your gall water or one color of paint can give an intriguing, crunchy texture to a marbled design.


on alum

I’ve recently undertaken a series of tests, as scientific as I can make them, to answer some questions I commonly receive from students and satisfy my own curiosity.

Firstly:  What is the difference between the various types of alum?

If you have done any natural dyeing or marbling, you have most likely used alum as a mordant. Alum is a metallic salt which bonds to both the fiber substrate and the coloring agent, creating an insoluble bridge linking them together.  Whether you are using dyes or paints on fabric or paper, an alum mordant will increase the amount of color that can latch on, and improve the washfastness and lightfastness of the finished piece. Alum is the most commonly used mordant because it is inexpensive, colorless, permanent, and toxic only in large doses.

I, like many marblers and dyers, am in the habit of using the term ‘alum’ to refer to two different compounds: potassium aluminum sulfate and aluminum sulfate. These two metallic salts function essentially the same way for mordanting, but it's worthwhile to consider their differences. I will not include aluminum acetate in this discussion, as it is always specified by name and is not in common use for marbling paper.

marbling tools.jpg

Potassium Aluminum Sulfate
Historically called potash alum, potassium aluminum sulfate is a translucent white crystalline powder.  It is naturally occurring, and has been extracted from alunite in volcanic areas since at least 1500 BC for purifying water, as a styptic, and a mordant. Today it can be refined from bauxite or alunite, or made in a laboratory by adding potassium sulfate to aluminum sulfate. Potash alum is the historical mordant called for in traditional dye and marbling instructions, and in making lake pigments from natural dyes.

Aluminum Sulfate
Aluminum sulfate can be made in a laboratory or refined from various types of stone. In appearance its crystals are jagged, with an opaque white dustiness. Since its introduction as an industrial product in the 19th century, it has replaced potash alum in many applications such as water purification and paper sizing, and is sometimes called papermaker's alum.

What's the difference?

  • Potash alum and aluminum sulfate may be used interchangeably as a mordant on both cellulose and protein fibers.
  • Potash alum is slightly more expensive.
  • Some dyers claim that potash alum gives clearer colors, but I have not noticed any difference between the two. If you have trouble with muddy colors, make sure your alum is from a reputable vendor. Any impurities, such as iron, will sadden your colors.
  • If you are forging historical artwork, using aluminum sulfate to mordant is a dead giveaway.
  • Both potash alum and aluminum sulfate are acidic. Whichever you use, follow mordanting instructions to avoid making your artwork overly acidic and brittle.
  • Most important for practical purposes: Aluminum sulfate is more water-soluble at room temperature. When mordanting paper, most historic manuals call for heating the water before adding potash alum (they don’t specify which alum, but potash alum is implied). Heating the water will allow the potash alum to dissolve quickly.
alum solubility chart

I made this chart from what scant data I could find, showing the solubility of both sorts of alum in one pint of water. Paper marblers generally use between 1-4 tablespoons of alum per pint, or about .5-2 ounces. Though both potash alum and aluminum sulfate are soluble at room temperature in that amount, in my experience warm tap water helps to speed up the dissolution of the crystals.

Please be in touch if you have any information to contribute, or reading to recommend! The alums and their history are a big topic.