The Grantville Gazette Vol 5 Part 21

We should also be able to learn how to make tempered gla.s.s. The gla.s.s is heated to a high temperature and then cooled rapidly. The process increases the strength of the gla.s.s several fold, and also alters how it breaks; it powders, rather than forming dangerous shards. The duplication of tempered gla.s.s is a matter of determining, whether by library research or experiment, the necessary parameters, such as tempering temperature and cooling rate.

Both auto winds.h.i.+eld "safety gla.s.s" and "bulletproof" gla.s.s are actually laminates of gla.s.s and plastic, and therefore must await the creation of a plastics industry.

Fibergla.s.s One of the largest twentieth-century markets for gla.s.s is in the manufacture of fibergla.s.s. Coa.r.s.e gla.s.s fibers were made and used in pre-Roman times, but merely for decoration of tableware. In 1870, John Player developed a process for ma.s.s producing a gla.s.s wool, useable as insulation. A fire-r.e.t.a.r.dant cloth, with interwoven silk and gla.s.s fibers, was announced by Herman Hammesfahr in 1880.

Grantville's Encyclopedia Britannica briefly describes a method of making fibergla.s.s in which the liquid gla.s.s enters a spinning, perforated cup, the fibers are extruded through the holes, and blasts of air fragment the fibers. Another approach, set forth in the World Book Encyclopedia, is to melt gla.s.s marbles in a furnace with a perforated bottom, and collect the threads onto a spinning drum. The tension created by the pulling drum helps draw out fine gla.s.s fibers.

The USE should be able make simple gla.s.s wools and cloths, but fibergla.s.s composites, such as those used in the hull of the speedboat Outlaw, require a mature plastics industry.

Military Mirrors There are some military uses of mirrors which were not well established in 1632, but which could now be exploited by the USE. These include the following:

Periscopes The trench periscope, used extensively in World War I, was invented by the Polish astronomer Johannes Hevelius (1611-1687) in 1637. The first naval use of the periscope was in the American Civil War, where one was improvised by Chief Engineer Thomas Doughty of the Union ironclad USS Osage during the Red River campaign of April 1864. (A periscope would have come in handy during the Monitor-Merrimac engagement, as Captain Worden of the Monitor was blinded when a sh.e.l.l struck near the viewing slit of the pilot house.)

Heliographs In essence, the heliograph communicates coded messages in the form of light flashes. The princ.i.p.al advantage of the heliograph over the electrical telegraph has been that it could be used even in hostile territory, where a telegraph wire had not yet been laid, or was likely to be cut. This is not a problem with radio communications, but the number of radio sets in the USE is limited. The heliograph was used to great advantage by the British in Afghanistan and in the Boer War, and by the Americans in the Indian Wars.

The Indian tribes had countered the electrical telegraph by cutting telegraph wires and poles; the mirror telegraph was much less vulnerable to enemy action. The Apaches understood the significance of the heliographs all too well; they avoided the territory crisscrossed by the heliograph network. (Rolak).

The signalers were typically 25-30 miles apart, and could send messages over distances of 800 miles in less than four hours. (Wrixon, 435). The average speed of the system was reportedly 16 words per minute. (Holzmann). In 1894, the U.S. Army set a new heliograph distance record (183 miles).

The 1865 Mance heliograph had a tripod-mounted mirror linked to a key mechanism. The key tilted the mirror in and out of position, causing it to flash on and off. (Plum, 30). In a late nineteenth-century U.S. army design, light flashes were achieved by coupling the key to a shutter placed in front of the mirror. Some versions of the Mance heliograph had two mirrors. Just one mirror was used if the sun were in front of the sender. If the sun were behind the sender, the second mirror could be positioned to reflect the sunlight onto the one facing the recipient. (Wrixon, 433).

Rangefinders A simple rangefinder uses two mirrors. One mirror, at one end of the baseline, is fixed at a 45 degree angle to the baseline. This stationary mirror is silvered on the bottom half but clear on the top half. The other mirror, at the other end, is a normal mirror, and is mounted so it can rotate. Look through the clear half of the fixed mirror at the target, then turn the rotating mirror until the object is visible in the mirrored half of the fixed mirror, too. A curved scale is used to trigonometrically convert the angular position of the rotating mirror into a distance to the target. The accuracy of the distance measurement is dependent on the length of the baseline; the longer it is, the better.

The first use of the rangefinder was in the military. According to W.L. Ruffell, "No serious attempts to obtain ranges by instrumental methods were made before 1770. That year saw the short base method put to limited use, e.g. for siege purposes, but it was a time-consuming process. Development of efficient optical rangefinders did not commence until 1860, at the start of the rifled era, and culminated in the introduction of the well-known Barr & Stroud types 20 years later."

Industrial Mirrors By 1632, concave mirrors had been used to melt metals and to heat liquids (b.u.t.ti, 33-34). Solar energy, concentrated by concave mirrors (or by biconvex lenses made of good optical gla.s.s), can be used to power solar stills, solar water heaters, solar cookers, solar pumps, and solar furnaces. (b.u.t.ti; EA "Solar Energy"). This may not be very attractive in northern Europe, but some of the USE commercial ventures will be in tropical regions where sunlight is intense. Solar energy is particularly attractive in arid regions where there is no inexpensive alternative fuel.

Selected References Available in Grantville "Industrial Gla.s.s," "Ravenscroft, George," Encyclopedia Britannica (EB) "Alkali Manufacture," "Aluminum," "Boracite," "Borax," "Boric Acid," "Colemanite," "Gla.s.s," "Kaolinite," "Lead," "Panderma," "Pota.s.sium," 1911 Encyclopedia Britannica (1911 EB) "Boron," "Borax," "Gla.s.s," "Kernite," "Solar Energy," Encyclopedia Americana (EA) "Fibergla.s.s," "Gla.s.s," World Book Encyclopedia (WBE) "Gla.s.s," Collier's Encyclopedia (CE) Savage, Gla.s.s of the World (1973) (p. 45 says that French cast plate gla.s.s onto a copper bed) Papert, The Ill.u.s.trated Guide to American Gla.s.s (1972) (1865 recipe for crystal gla.s.s on p. 2.)

General References on Gla.s.s and Gla.s.smaking Douglas and Frank, A History of Gla.s.smaking (1972) Hynd, "Flat Gla.s.s Manufacturing Processes" (Chap. 2), and Wilson, "Tubing and Rod Manufacture" (Chap. 4), in Vol. 2, Processing I, of Uhlmann and Kreidl, Gla.s.s-Science and Technology (1980) "Gla.s.s," in the Kirk-Othmer Encyclopedia of Chemical Technology Ellis, Gla.s.s: From the First Mirror to Fiber Optics, The Story of the Substance That Changed the World (Avon Books: 1998) Macfarlane and Martin, Gla.s.s: A World History (U. Chicago Press, 2002) Polak, Gla.s.s: Its Tradition and Its Makers (G.P. Putnam's Sons: 1975) Diamond, The Story of Gla.s.s (Harcourt, Brace: 1953) Mehlman, Phaidon Guide to Gla.s.s (Prentice Hall: 1983) "The Inventor of Float Gla.s.s,"

Pilkington company history,

BBCi, "Historic Figures: Sir Alastair Pilkington," http://www.bbc.co.uk/history/historic_figures/pilkington_alastair.shtml "Float Gla.s.s"

Reat and Munley , "Justus von Liebig: An Educational Paradox," http://step.sdsc.edu/projects95/chem.in.history/essays/liebig.html Smith, "Borax in Gla.s.s-Ancient or Modern?", Pioneer Magazine (January 1997), online

Chap. 18, "Spot and Roebuck (Acid)," in Caveman Chemistry

Barbour, Gla.s.sblowing for Laboratory Technicians (1978)

References on Uses of Gla.s.s Gregory, Mirrors in Mind (W. H. Freeman, 1997) Newman, The Mirror Book: Using Reflective Surfaces in Art, Craft, and Design (Crown Pub., 1978) Schiffer, The Mirror Book: English, American & European (Schiffer Pub., 1983) Melchior-Bonnet, The Mirror: A History 18 (Routledge: 2001) Van den Muijzenberg, History of Greenhouses (1980) b.u.t.ti and Perlin, A Golden Thread (1980) Holzmann, "MEMS the Word," Inc magazine (Nov. 15, 2000), Rolak, "The Heliograph in the Geronimo Campaign of 1886." Military History of the Spanish-American Southwest: A Seminar. Ft Huachuca, AZ, 1976.

Wrixon, Codes, ciphers & other cryptic & clandestine communication: making and breaking secret messages from hieroglyphs to the Internet (Black Dog & Leventhal Publishers : 1998).

Ruffell, "The Gun: sights and laying-rangefinding" (1996);

Miscellaneous References Hochleitner, Minerals: Identifying, Cla.s.sifying, and Collecting Them Fontana, Corrosion Engineering (1986) Winder, "The History of Lead"

Lambert, Tracing the Past: Unraveling the Secrets of Archaeology Through Chemistry (Perseus Books: 1997) "Boron Compounds (Oxides, Acid, Borates)," in the Kirk-Othmer Encyclopedia of Chemical Technology

Dyes And Mordants

By Lisa Satterlund

I. Introduction and brief history of dyeing.

By 1630, human beings had been using plants, animals and minerals to change the natural color of plant and animal fibers for at least five thousand years. The oldest written record of dye use goes back to 2,600 BC in China, and archaeologists have identified dyed textiles from about 1,400 years earlier than that. Vastly more is known about commercial dyeing than is known about early modern home dyeing. That doesn't mean that a lot is known about either. Dyeing was considered as much an art as painting, and rarely was the process doc.u.mented before the latter part of the eighteenth century. Major sources of information about dyeing prior to that date are two dyers manuals that were published in the fifteenth and sixteenth centuries, ma.n.u.scripts containing dye recipes other than the dyers manuals and economic records of towns and guilds. Next to nothing is known concerning home-dyeing prior to the revival of natural dyeing in the 1960s.

The first European commercial dyer's guide, Mariegola Dell'Arte de Tentori, was published in the early fifteenth century. Earlier works mentioned dyestuffs, the dye industry, and an occasional dye recipe. For example, a Greek ma.n.u.script known as the Stockholm Papyrus contains a recipe for imitation purple, and an Egyptian papyrus of 236 BC mentions dyers. Pliny the Elder talks about dye plants and bleaching with sulfur. For the most part, however, actual dye recipes were rarely printed. Dyers considered themselves artists, and guarded their recipes carefully. Years of development could go into the formulation of a good black dye, for instance, which would put that dyer's goods in great demand. Since reproducing colors with natural dyestuffs is never easy, the dyer could be fairly certain to maintain his position of superiority as long as the recipe did not become known.

The earliest colors that rated mention by ancient writers were reds, purples and blues; all dyed using natural materials that are known today and were major dyestuffs until the discovery of the first synthetic dye in 1856. Other subjects that ancient writers mention indicate that techniques such as printed fabric and batik are hundreds, if not thousands, of years old, as well.

Two major events in the history of dyeing during the early seventeenth century were the discovery of the effects of the use of tin as a mordant in 1630 by a Dutch chemist, and the beginning of the East India Company's importation of calico from India in 1631. The discovery that the Indians were able to produce brilliant colors and fancy patterns on cotton resulted in a drive by European dyers to reproduce the effects.

II. Dyeing.

A. Before the fact.

Plant and animal fibers can be dyed in the fiber (raw), as yarn or as fabric. The process for preparing the fiber for dyeing varies only slightly for the different forms, but can vary quite a lot between fibers. Linen and silk were rarely dyed raw, due to the vagaries of processing these fibers. The natural color of most wool, stream-retted linen and silk is slightly yellow. Dew-retted linen is grayish. For the sake of simplicity, this article will refer throughout to fabric as the item being dyed. Also, please look to the glossary at the end for definitions of dyeing terms.

The first step in preparing the fabric for dyeing was scouring. For wool this meant was.h.i.+ng in stale urine or a solution of potash and water to remove the natural oils still present, as well as any oils added during processing. Even where the wool had been scoured on the sheep or in the raw, dirt was inevitably picked up during the weaving and had to be removed before dyeing. The ammonia in the urine and potash mix acted as a detergent.

Silk had to be cleaned before weaving, as in its natural state it was coated with a waxy substance called sericine, which made the fiber sticky and gave it a harsh feel. The method was fairly simple: the silk was boiled in a soapy solution for a number of hours. The removal of the sericine took most of the yellow coloring with it. The same process was followed after weaving to remove whatever dirt and oils were acquired during processing.

Cotton and linen, which not only contained natural waxes but were often coated with sizing during weaving, were fermented by adding bran to warm water into which the fabric was packed. Weights held the fabric down during the fermentation process, and it was important to remove the fabric before the sc.u.m created during fermentation settled into the fibers.

Once the fabric was clean, it was time for bleaching. Cotton and linen were almost always bleached before dyeing as the bleaching process helped a.s.sure that the fiber or fabric would dye evenly. Wool and silk were generally only bleached if they were to be dyed a light color. "Black" wool, which could be any color from tan to dark brown, would be used in its natural state.

Silk and wool were bleached by means of sulfur fumes. The wet fabric would be hung in a special room with pots of sulfur set on the floor. The sulfur would be lit and the room sealed until the sulfur burned out. This process was much faster than the method used to bleach cotton and linen, but was considered less satisfactory because sulfur-bleached fabric tended to turn yellow if not carefully handled. In addition, this method of bleaching did more damage to the fibers. While it is unclear how old this method is, the Roman Pliny mentions the use of sulfur for bleaching.

Cotton, linen and hemp, all cellulose fibers, were bleached in basically the same way. The fabric would be soaked in a mildly alkaline solution (often made from "rotten urine" or potash dissolved in water), removed and rinsed, then spread out in the sun. Depending on the time of year, the fabric would be moistened by dew or by being sprinkled with water. After some time in the sun, the fabric would be rinsed again, soaked in a mildly acid solution (often sour milk), washed, then returned to another alkaline bath. This process of alkaline bath, sun exposure, acid neutralization and was.h.i.+ng would be repeated eight or more times, depending on the degree of whiteness desired. The entire bleaching process could take as long as eight months to complete.

B. Dyeing Now the fabric was ready to be dyed. The first step was to obtain the dye. Commercial dyers bought theirs in the form of cakes, dried plants or wood chips. Home dyers, on the other hand, would have to gather the plants, lichens or other materials. This meant they needed to know which parts of which plants would produce the colors they were striving for.

Next, the dyer needed to prepare the dyebath, either by boiling and straining plant matter or by grinding prepared dyestuffs. Commercial dyers needed to know how many pounds of dyestuff were needed to dye large amounts of fabric, and trusted to experience (and the sellers of the dyes) for that information.

While the dyebath was being readied, the fabric was prepared for dyeing. Since it was received by the commercial dyer already scoured and bleached, the only step necessary was mordanting. A mordant is a chemical (most commonly a metal salt) that helps the dye adhere to the fabric. Fabric could be mordanted before, during or after dyeing. Since fabric was never dyed dry, it was common to use a mordant bath to wet the fabric before dyeing.

Once the dyebath was ready, the wet fabric would be lowered into it. The fabric would be drawn repeatedly through the dye to insure that the color would take up evenly. When either the desired color was achieved or the dyebath was exhausted, the cloth would be removed, rinsed thoroughly, and dried. Some colors required the fabric to be dyed multiple times.

III. Materials A. Equipment and requirements (tools, fuel, location) The two most important requirements for a dye house were plenty of clean, soft water and plenty of fuel. The location of the dye house was determined by this need for water and fuel. Dyeing required so much fuel, in fact, that many localities tried to limit the amount of wood bought by the dyers, restrict where it could be purchased, or ban the use of certain types of wood.

Ideally, a dyehouse had both a well with a pump and a system of pipes and troughs, and a nearby river. Soft water was preferred, as the minerals in hard water could affect the dye colors and the ability of the fabric to absorb the dye. The river was often used for was.h.i.+ng fabrics (before or after dyeing) with the aid of a "dyer's raft" anch.o.r.ed in the river. There is record in the Hamburg archives concerning a hearing held to determine whether the dyers should be permitted to anchor a new raft after the old one was swept away during a flood. The council listened to testimony from local fishermen about the deleterious effect of the raft on the fish population. In the end, a new raft was permitted, but the dyers were forced to move it down steam, past the fis.h.i.+ng grounds.

In addition to water and fuel, the dyers needed copper vats for preparing dyebaths, wooden vats for dyeing the fabric, furnaces for heating the water and boiling the dyes, hooks, rods, barrows and winches to move the fabric around, tools for grinding the dyestuffs, the dyestuffs themselves, mordants, and a building large enough to use and store it all. The building had to have a stone floor with provision for draining water and separate rooms for drying wet fabric and for storage. The roof had to be vented to allow steam and fumes to escape. Often, there would be a separate shed for storing fuel.

Setting up a dye house was an expensive proposition. In Nuremberg during the middle of the sixteenth century, the city council ordered a dyehouse built, with estimated construction costs of three thousand guilders. This was part of a series of expenditures made by the council to lure dyers from Antwerp to Nuremberg. All told, the council's investment totaled more than ten thousand guilders.

Home dyeing was simpler. All that was necessary was a pot for preparing the dyebath and some utensils for handling the hot, wet fabric. The modern home dyer uses inert pots and utensils dedicated to dyeing. The early modern home dyer probably used iron pots; whether these were dedicated to dyeing is unknown. The wet cloth could be lowered into the dyebath by hand, but once there a spoon or paddle would be needed to swish the cloth about and insure the color was absorbed evenly. Useful, but not required, would be some type of roller or wringer to squeeze excess dyebath from the cloth when it was done. Lastly, a place was needed to hang the finished product where it would be protected from dirt and dust while it dried.

B. Dyestuffs and mordants i) Dyes: Dyestuffs could be found everywhere, but since most produced various shades of yellow and brown, those that produced reds, purples and blues were more valuable. After the discovery of the Americas in the fifteenth century and the establishment of the English East India Company in 1600, more exotic colors were available. Explorers were so aware of dyestuffs as trade goods that the country Brazil was named after the abundance of brazilwood found there. Not all the exotic dyestuffs were worth using, however. The red produced by brazilwood, for example, is fugitive, as is the lavender that comes from logwood.

The most common sources for reds, purples and blues during the early modern period were madder (red), murex (so called "imperial purple"), kermes (red), orchil (purple), woad (blue) and indigo (blue).

During the period between 1624 and 1627 in Frankfurt am Main, the cost of various dyestuffs ranged from about seven guilders per hundredweight for madder to two hundred and twenty guilders per hundredweight for indigo from Dominique. Between those two extremes, prices are recorded for galls from Aleppo at twenty-four guilders per hundredweight, woad from Erfurt at sixty guilders per barrel (approximately sixty pounds) and cochineal from Poland at about nine guilders per pound. Thus, it is clear that the price of the various dyestuffs varied widely.

The most expensive colors were black, blue and dark green, all of which required bottoming with woad or indigo first. The highest quality blacks were produced by "bottoming" fabric with woad until it was a very dark blue, then overdyeing it with madder. This combination made a color very close to a true black. Blue used woad or indigo alone, and dark green was produced by overdyeing blue fabric with weld, dyer's greenweed or a similar yellow dye.

Cheaper methods did exist to produce dark colors. Galls mixed with iron filings made black, black walnut sh.e.l.ls produced a good brown, yellow bedstraw and safflower (when prepared as a vat dye) produced red. The home dyer may have experimented with reds and purples from beets and berries, too. Unfortunately, time has shown that these last produce only fugitive colors. Some of the colors produced by these cheaper methods were as good as the more expensive dyestuffs. Some, however, were not. Dyes containing too much tannic acid or iron damaged the fabric, eventually causing the fabric to disintegrate. Safflower red, like the berry colors, was fugitive.

Dyes such as galls, sumac, vitriol were banned in many cities and called "devil's colors" because of the damage they did to the fabric. As a measure to protect the woad trade, indigo also appeared in most lists of "devil's colors," even though it did not damage the fabric and, in fact, was a more efficient dye than woad.

ii) Mordants: In fact, most dyes were fugitive without the a.s.sistance of a mordant. Most mordants are metal salts, although there are a few, like tannic acid and tartartic acid, that are not. During the early modern period, the most common mordants were alum, copperas (iron) and blue vitriol (copper). All of the metal-salt mordants were toxic to some degree. Disposal of mordant baths and spent dye liquor into the nearest river led to fish kills and unnaturally colored streams.

A number of other chemicals were used in a.s.sociation with mordants, such as cream of tartar, urine, salt and vinegar. Some of these chemicals helped balance the pH of the dyebath while others helped a.s.sure the color was taken up evenly. The desired pH of the dyebath depended on the fiber being dyed, since silk and wool take color better in an acidic bath, while cotton and linen require an alkaline bath.

Fabric could be mordanted before, after or during dyeing. Most commercially dyed fabric was mordanted before dyeing, and then sometimes mordanted again, with a different salt, after dyeing. The combination of mordants and when they were applied both affected the final color. Many dye recipes from the Innsbruck ma.n.u.script, which contain the earliest known dye recipes in the German language, call for two or three different mordants to be applied.

Some dye plants also act as mordants, and would be easy for the home dyer to obtain. These include oak leaves, bark, galls and nuts, sumac or alder leaves, and black walnut sh.e.l.ls. All of these alone produce brown and tan dyes. When combined with other colors, they would darken the original color. In addition, by using a copper or iron pot, the home dyer could simultaneously dye and mordant, thus saving a step in the process. Some modern dyers claim that dyeing in a reactive pot does not provide enough mordant to insure that the color will remain fast.

Club moss and seaweed, which contain alum, were also available to the home dyer, and where old wine barrels were accessible, the cream of tartar could be sc.r.a.ped from the inside of the barrels and added to the dyebath. Urine would also be a common mordant for the home dyer. It works better with some dyes than with others, and certain dyes, such as woad, require it. However, woad is not a mordant dye in the usual sense. It is a vat dye. The coloring agent is insoluble in water, and the dyebath is a solution of wood ash and rotten urine in which the woad has been fermented.

In addition to helping the dye bond with the fiber, mordants can change the color of the final product. Copperas (iron) and blue vitriol (copper) are said to "sadden" colors because they darken them and make them dull. Alum has very little effect on the color, which is one of the reasons it was so popular. Tin, which was first used as a mordant in 1630, brightens or "blooms" colors. Tannic acid tends to make colors brown. Other chemicals, while weak mordants by themselves, can be used to alter the effect of traditional mordants. Adding ammonia and probably urine causes yellow dyes to turn greenish. Vinegar both brightens and darkens colors.

The choice of mordant can make a dramatic difference in the final color obtained. Wool dyed with Dyer's greenweed and mordanted with alum produces a clear yellow, while wool mordanted with tin produces a dark blackish brown. Copper as a mordant with this plant and wool gives the yellow a greenish tinge.

Most mordants were sold by the hundredweight, with prices at Frankfurt am Main ranging from five guilders per hundredweight for Austrian red cream of tartar to thirty-three guilders per hundredweight for Aleppo galls. It is clear from the prices that quality varied with location. The price for Dutch alum ranged from seven to nine guilders per hundredweight, while the price for Bohemian alum was twice that.

Dyes and mordants were generally used at near boiling temperatures, filling the dyehouse with steam and fumes. Some of the materials in use, such as urine and fermenting plant matter, stank even at low temperatures. The addition of heat caused some volatiles to boil off, increasing the smell. Between the smell and the damage to nearby streams, dyehouses were not popular neighbors.

iii) The fiber: For the most part, dyestuffs produced the same colors no matter what fiber the fabric was made of. So woad and indigo turned cotton and linen, as well as wool, blue. Wool is the easiest fiber to dye, whether in the hands of the commercial or home dyer. It takes color well and is very reactive to the different mordants. Silk is also easy, and the colors, while perhaps not as deep as those in wool, are very vibrant. Both of these are protein fibers. Cotton and linen, on the other hand, are cellulose fibers, and until chemists and dyers unlocked the secrets of the Indian dyeing industry, cotton and linen tended to be paler and less vibrant. Fabric wasn't the only thing being dyed. Recipes exist for dyeing feathers, leather, wood and food.

IV. Applications While keeping in mind that no up-timer has knowledge of early modern dyeing, there are still areas in which Grantville's collective knowledge of modern chemistry could lead to changes and improvements. The following are some suggestions.

Speeding up the bleaching of cotton and linen. The article on bleaching in the 1911 Encyclopedia Britannica can be used as a starting point. That article traces advances in fiber bleaching.

Improving the purity of mordants. Mordants which could be relied upon to act in specific ways would be in high demand by dyers.

Improving the purity of dyes from woad and indigo. Synthetic indigo took a long time to develop. In the meantime, a dye of known strength and reliability would be a source of income for the developer.

V. Glossary A. Terminology Adjective dyes: Dyes that require the presence of a mordant.

Bleaching: Removing the color from fiber. The people who did this were bleachers.

Bloom: The brightening of a dye by choice of mordant.