Pigments are like tiny, inert, colored rocks. Because pigments do not react chemically with anything, they tend to be very light fast, resisting fading in sunlight. Pigments can become 'paint' when suspended in a binder such gum arabic for watercolor paint or acrylic medium for acrylic paint. Pigments are also an excellent material to color paper pulp. When pigment is used to color paper pulp, however, it is suspended in water with no adhesive-like binder as in paint.
Pigments are very easy to use, and they mix together well in order to create subtly colored pulps. Primary pigments, such as yellow and blue, can be combined to create secondary colors, like green, before OR after the pigment is added to the pulp. For example, yellow pulp can be mixed with red pulp to create orange pulp. Several pigments or colored pulps can be mixed together to create taupe or mauve.
THE PRINCIPLES OF COLORING WITH PIGMENT:
Pigment sticks to paper pulp through a '+' and '-' attraction, a little like a magnet. The cellulose plant fiber (pulp) is anionic; which means that it has a negative charge which increases from the pounding or beating of the fiber during pulp preparation in the hollander beater. Dry, unbeaten, fiber has very little or no charge. As the fiber is beaten into a pulp, the '-' charge increases. Pigments have little attraction to the pulp, so a material which has a '+' or positive charge must be added. Retention agent is such a material, and its only purpose is to provide the '+' charge. Internal Sizing is a mild waterproofing agent which also happens to be cationic; it has a positive '+' charge. Consequently, Internal Sizing adds both waterproofing properties AND retention properties.
The positive charge of the fiber depends on how much the fiber has been beaten in the pulping process, the longer it is beaten the greater the charge. Cationic materials (with a '+' positive charge) add to the charge. If you pour in too much retention
agent, however, you can add too much '+' charge, the poles on the little magnets will reverse, and all the pigment will instantly come off the pulp. If this happens, just rinse the pulp, washing away the pigment and excess retention agent. Then add more pigment. You may not need anymore retention agent as there may still be enough on the fiber. If you feel like you need more, just add a tiny amount and dilute it a lot before adding it.
DIRECTIONS FOR COLORING PULP WITH SIZING AND RETENTION AGENT:
At Twinrocker, we color with pigments by first sizing pulp made from 3 pounds of dry fiber (1 beater load which is one 5 gal. pail of ready-to-use pulp) with 50 ml. or 5 tbsp. of our Internal Sizing. We dilute the measured sizing in plenty of water (about a quart) and slowly add it to the pulp while stirring to mix it in evenly. This sizes the pulp and adds some '+' charge.
We then add the pigment to the pulp. A tiny amount of red will create a pink pulp, more red, a more intense color. The liquid pigments are very concentrated, so begin by adding just a little. If you want an intense color, add a little pigment and mix it into the pulp well before you add more. Gradually build the intensity of the color . If you find you've added too much pigment for the color you want, just add more white pulp to make the color more pastel. After stirring the pigment into the pulp thoroughly, it should automatically stick to the pulp, and the water should be clear or almost so. If you still have pigment in the water after you have stirred the pulp thoroughly by hand. The pigment has attached to most of the bonding sites on the fiber, and little if any more pigment will stick to the pulp. It is that simple. No rinsing is needed after coloring.
If the pulp has not been beaten very much and does not have a strong '+' charge, we then add a very dilute liquid retention agent (perhaps a tsp. in a quart of water). We add it slowly while stirring so that the '+' charge is mixed in the pulp evenly and stop when the color begins to attach to the pulp. If the color is too intense, you can lighten it or make it more pastel by adding white pulp.
Those who are not pulping cotton linters in a hollander beater, but in a mixer or blender instead, color their pulp using retention agent in a slightly different manner. They dilute the pigment they want to use with water, then add a little retention agent to that pigment/water mixture, and then add that mixture to the pulp. If you are having trouble coloring fiber that has not been beaten in a hollander, try using our dry, powdered retention agent as it is stronger than the liquid material. We have found that the dry material tends to 'overcharge' fiber prepared in a hollander, however.
COLORING PULP WITH PIGMENTS IS
EASY AND LOTS OF FUN!
This is a fairly detailed explanation of how pigments stick to paper pulp, but I could have said, 'It's magic.' That's how spontaneous and easy it is to do. Mixing colored pulps together to create art work is as easy as mixing colored paints together. If you should have a problem, just give us a call at Twinrocker, and we'll be happy to help you.