See cellulose acetate

CH COOH; an organic acid; also called (rarely) ethanoic acid 3 Glacial acetic acid (GAA) is commonly sold for industrial purposes. It is almost pure acetic acid (that is, it contains almost no water), pungent smelling and flammable. It is called "glacial" because it will freeze at around 17°C. Concentrated solutions of acetic acid are dangerous, and must be handled with care. Acetic acid is used in many dyeing processes. It is much less expensive than vinegar where large amounts are required. Often a 56% solution (in water) is called for. Acetic acid is a weak acid (see acid, weak - this does not mean "mild").

A chemical that will produce a pH of less than 7 in water solution Many acids are used in dyeing. They include acetic acid, citric acid, formic acid, hydrochloric acid and sulfuric acid. Several other compounds, such as sodium bisulfate and ammonium sulfate form acids in solution through hydrolysis. When making solutions of acids or when diluting concentrated acids, always add the acid to water, never the other way around. This is because some acids produce a great deal of heat when they mix with water - so much that a small amount of water added to a large amount of acid may actually boil and cause extremely dangerous spattering.

A compound that hydrolyzes or breaks down to yield acid In a number of dyeing and printing processes, primarily with acid dyes, there are advantages to starting with a bath or print paste that is pH neutral or only slightly acid, but that will become more strongly acid as boiling or steaming progresses. Acid donors, such as ammonium sulfate or ammonium tartrate are often used for this purpose.

A large class of dyes that are applied from acidic solutions to polyamide fibres These synthetic dyes are used for wool, silk and nylon. They are typically applied in a bath that may range from strongly acid to neutral, and usually at temperatures approaching boiling. Bonding between the dye and fibre can be complex. Some form ionic bonds between basic groups of the fibre and acid groups of the dye, but other bond types occur. There are a great many acid dyes, in a number of major sub-groups, with a wide variety of properties. Included are “washfast acid dyes”, “milling dyes”, “supermilling dyes”, “leveling acid dyes”, “1:1 premetallized dyes”, “2:1 premetallized dyes” and others (the premetallized dyes are sometimes regarded as being in a class of their own, apart from acid dyes). The distinction between some of the groups is often vague. Acid dyes range from poor to excellent colorfastness, and from dull tones to brilliant shades. The choice of sub-group is often a compromise among the characteristics of colorfastness, leveling properties and shade availability. Acid dyes may not perform well in mixtures, even with dyes from the same general class, so care is required in selection.

A strong acid virtually completely ionizes in solution. All of the acid, represented by HA, exists in solution as H+ (or H 0+ - the hydrogen ion combines with a water 3 molecule to make a ion called hydronium) and A-. Hydrochloric acid and sulfuric acid are common strong acids. Note that even in very dilute solution, these are still regarded as strong acids.

A weak acid is an one that does not fully ionize in solution Some of the acid remains in molecular form, rather than completely ionizing. If HA represents the acid, some would remain in solution as HA, and some would ionize to H+ and A-. Acetic acid and citric acid are commonly used weak acids. An acid may be technically weak, but still capable of causing serious skin burns. See acid, strong. See base, weak for more discussion of pH effects surrounding “weakness” (remembering that more acid lowers pH).

With reference to textiles, a synthetic polymer fibre made from acrylonitrile compounds. Acrylic is probably the most popular synthetic fibre for yarns for hand knitting. It is also used for fleece clothing. Modacrylic is acrylic that contains other monomers to alter some properties, such as flame retardancy. Acrylic is normally dyed with basic dyes. The process requires care get level results and to avoid damage to the fibre.

Attraction between two items; in dyeing affinity essentially means the preferential attraction of the dye for the fibre rather than for the solution of the dyebath A dye with high affinity readily leaves the dye solution of dispersion to attach to the to the fibre being dyed. This does not necessarily imply that the attachment of the dye to the fibre is strong. Technically, affinity is expressed in terms of energy. It is determined under standardized conditions, so it is incorrect to say that affinity is altered by auxiliary chemicals or the like. See substantivity.

An extract of seaweed used as a thickener “Sodium alginate” is used in textile printing pastes, and sometimes to thicken dye solutions for direct application. It is a preferred thickener for reactive dyes because it does not react with, and therefore use up, the dye. It comes in a number of variations that have somewhat different properties. “Low viscosity” types are appropriate for reducing migration of wet dye solutions for fine line work, while “high viscosity” are more suitable for making printing pastes. It can form gels at low pH or very high pH, so it is not suitable for some print paste formulations.

A subclass of base, though often used to refer to any base Partly because the term “basic” is often rather confusing, “alkaline” is often used to refer to solutions that are basic - having pH greater than 7.

A term for a variety of chemicals, with a lot of potential for confusion There are several compounds that are called alum. One is aluminum potassium sulfate - pickling alum. Others include aluminum sulfate (the alum most used in textile arts, and used in municipal water filtration plants), aluminum ammonium sulfate (ammonia alum), chromium potassium sulfate (chrome alum), and more. Some alums are used as mordants in dyeing, primarily with natural (plant extract) dyes. Aluminum sulfate is often used in marbling.

Aluminum is included here because many pots are made of aluminum. In general, aluminum is not appropriate for dyeing vessels. It is attacked by both acids and bases, and explosive hydrogen is liberated in the process. Also watch out for aluminum rivets used to hold the handles on some stainless steel pots.

“pickling” alum; AlK(SO ) 4 2 This is the alum available from the grocery store.

Al (SO ) ; an “alum” 2 43 Aluminum sulfate is used in marbling with fabric paints. It will hydrolyze to become quite acid, which will destroy cellulosic fibres if given sufficient time, so it must be applied shortly before use, and rinsed out thoroughly afterwards.

A gas, NH ; often used to refer to a solution of ammonia in water, called aqua ammonia or ammonium 3 hydroxide (NH OH) 4 Ammonium hydroxide is sometimes used for pH control, mostly where the desired pH is only moderately basic. It is used in some stripping processes for acid dyes and in rinses for reactive dyes on wool. Ammonia vapors are very irritating, and solutions should be handled carefully.

(NH ) SO 4 2 4 Ammonium sulfate is a solid chemical that is used most commonly with acid dyes and 2:1 premetallized dyes. It decomposes through hydrolysis as the bath temperature rises, slowly releasing acid. This helps produce level results: at the start of dyeing the pH of the bath will be near neutral and will drop as dyeing progresses. Neutral conditions favor leveling, while more strongly acid conditions favor good exhaustion.

An enzyme that catalyzes the breakdown of starch Use of amylase enzymes is now the industrially-preferred way of removing starch sizing from textiles. The reaction with the enzyme essentially converts starch to water-soluble sugar. Unfortunately, amylase enzyme is difficult for the textile artist to obtain.

A starch made of long unbranched chains a-D-glucopyranose (which is quite similar to glucose, C H O ; 6 12 6 the “a” should be the Greek letter alpha, but that character may not appear properly on all computers) amylopectin - a starch made up of long branched chains of a-D-glucopyranose (which is quite similar to glucose, C H O )

Without water Many “dry” chemicals may contain some water as part of the crystal structure. Although this can often be compensated for in making up formulas, it is often more convenient to use chemicals that contain no water, that is, that are anhydrous. Many dry chemicals are hygroscopic. See hydration number.

C H N; also called aniline oil, benzeneamine, aminobenzene 6 7 Aniline used to be a very commonly used chemical in the synthesis of dyes. Sometimes the term ‘aniline dye’ is used as something of a catch-all term for synthetic dyes, though very few dyes still in production are actually aniline derivatives. Because of toxicity, aniline has been replaced with other compounds for most dye synthesis.

A negatively charge ion Many chemicals used in textile processing are described as anionic. This means that when the chemical ionizes in solution, the ion that is “functional” has a negative electrical charge. Most dyes are anionic. Surfactants, including some used as fabric softeners, may be anionic (others are cationic or non-ionic).

An additive used in dye or pigment mixtures to prevent undesired movement or spreading of the wet dye on fabric Anti-migrants are used in thickened dye solutions or dye pastes used for printing fabric so that the printed pattern will retain sharply defined edges. Sodium alginate is often used for this purpose for art processes. Antimigrants are also used in commercial pad-batch dyeing to prevent uneven shading across the width of the fabric.

A chemical used to neutralize chlorine bleach It can be very difficult to completely rinse chlorine bleach out of fabric. The residual bleach can interfere with subsequent dyeing, or can eventually damage the fibre. A rinse in a solution of antichlor, most commonly sodium bisulfite, will quickly neutralize the bleach. Hydrogen peroxide also functions to neutralize chlorine bleach. A thorough rinse is required after using antichlor. All of the common antichlor compounds essentially convert free chlorine bleaching agents to hydrochloric acid. If enough acid is produced, it can cause liberation of free chlorine gas, which can be hazardous and is certainly very irritating. Sodium carbonate added to the antichlor rinse will neutralized the acid. ACID RINSES, SUCH AS VINEGAR IN WATER, SHOULD NOT BE USED TO STOP CHLORINE BLEACHING. For neutralization of chlorine in water used to make up dye baths, sodium thiosulfate is the preferred antichlor agent.

Referring to a chemical compound which contains two nitrogen atoms with a double bond between them (-N=N-) “Azo” is used for a class of dyes based on (this) chemical structure. Azo dyes may be found among direct, acid, basic, reactive and disperse dye classes. Dyes with one pair of nitrogen atoms azo bonded are often called monoazo. Those with two or three azo bonded pairs are called disazo (not diazo) and trisazo, respectively. Do not confuse azo with azoic.

A term generally applied to a class of dyes based on application method; sometimes called naphthol dyes Azoic dyes are actually chemically synthesized inside the fibre, and are not truly dyes, but insoluble pigments. The soluble “naphthol” component is applied to the fibre, then a solution of “diazo salt” is used to develop the color. “Azoic” should be used only for this type of dye, not for azo dyes in general. These dyes are used commercially, especially for reds, but are not readily available to artists. The components used can be very toxic before they react to form the pigment.

A stripe-like or bar-like pattern in dyed fabric The dye uptake of some synthetic fibres, notably nylon, can be influenced by minor variations in conditions when the fibres are made. If yarns with these variations are made into fabric, then dyed, the result may be a bar-like pattern of darker and lighter shades or slight hue differences. Sometimes nylon is dyed with disperse dyes rather than acid dyes because the former are better at covering barré.

A chemical compound that will produce pH of greater than 7 in water solutions; alkali is often used synonymously, though this is not strictly true (all alkalis are bases, not all bases are alkalis); essentially the “opposite” of an acid By far the most common base used in dyeing is sodium carbonate (soda ash). Other bases used include sodium bicarbonate (baking soda), trisodium phosphate (TSP) and sodium hydroxide. Strong bases can cause serious skin burns.

A strong base fully ionizes in solution. See Base, weak. Sodium hydroxide is the most common strong base in textile processing.

A weak base does not fully ionize in solution. Some of a weak base remains in solution in molecular form. If BOH represents the base, some would remain in solution as BOH, and some would ionize to B+ and OH-. This makes for something of a "reservoir" action - if some of the OH- ions are used up in reactions, more of the BOH will ionize. Because of this, the pH of a solution of a weak base will change by less than one for a change in concentration of the base by a factor of 10 (for a strong base, which ionizes completely to B+ and OH-, increasing the concentration by a factor of 10 will increase the pH by 1).pH, unless very accurately measured, is a poor indication of how much of a weak base is in solution. Sodium carbonate and sodium bicarbonate are examples of weak bases (note that neither actually contains OH, but rather they hydrolyze to yield OH-). {Rev 3.0.0r}