Natural Dyes-Dyeing Processes, Chemistry tutorial

 

Introduction

Historically, natural dyes were utilized to colour clothing or other textiles, and by the mid-1800, chemists began producing synthetic substitutes for them. Through the early part of this century only a tiny percentage of textile dyes were extracted from plants. Lately, there has been rising interest in natural dyes, as the public became aware of ecological and ecological difficulties related to utilize of synthetic dyes. The employ of natural dyes cuts down considerably on the amount of toxic effluent consequential from the synthetic dye procedure. Natural dyes usually need a mordant that are metallic salts of aluminum, iron, chromium, copper and others, for ensuring the reasonable fastness of the colour to sunlight and washing.

Definition of Natural Dyes and Mordant

Natural dyes are a class of colourants extracted from vegetative matter and animal residues. A mordant is an element which aids the chemical reaction that takes place between the dye and the fiber so that the dye is absorbed.

Types of Natural Dyes

Natural dyes can be sorted into three categories: natural dyes obtained from plants (for instance indigo), those obtained from animals (for example cochineal), and those obtained from minerals (for example ocher).

Natural Dyes Obtained from Plants

(a) One instance of a natural dye attained from plants is madder that is attained from the roots of the madder plant. The plants are dug up, the roots washed and dried and ground into powder.

During the 19th century, the most broadly available fabrics were those which had been dyed through madder. Analyses of red fabrics found in King Tutankhamen's tomb demonstrate that they were dyed by madder, a plant-based dye. This red was considered brilliant and exotic. The madder plant continued to be utilized for dyeing until the mid-1800s when a synthetic substitute was extended.

(b) Another instance of a natural dye obtained from plants is woad. Until the middle Ages, Europeans employed woad to create a blue fabric dye. The woad was a shrub that grew abundantly in parts of Europe. The colouring was in the leaves that were dried and ground, mixed with water and made into a paste. This dye was supplanted via indigo, an ancient shrub well known to the Egyptians and Indians. As woad, its colour lay in its leaflets and branches. The leaves were fermented, the sediment purified, and the continuing material was pushed into cakes.

(c) Indigo prevailed as the desirered blue dye for a no of causes. It is a substantive dye, needing no mordant, yet the colour attained is enormously fast to washing and to light. The manufacture of natural indigo lasted well into the early 1900s. In 1905 Adolf von Bayer (the scientist who also formulated aspirin) was   awarded   the  Nobel  Prize  for  discovering  the  molecular structure  of  indigo,  and  developing  a  process  to  produce  it synthetically.

Natural Dyes Obtained from Animals

A good instance is cochineal that is a brilliant red dye generated from insects living on cactus plants. The properties of the cochineal bug were determined through pre-Columbian Indians who would dry the females in the sun, and then ground the dried bodies to manufacture a rich red powder.

When  mixed  through  water,  the  powder  produced  a  deep,  vibrant  red colouring. Cochineal is still harvested today on the Canary Islands. In fact, most cherries today are specified their bright red appearance through the artificial colour 'carmine' that comes from the cochineal insect.

Natural Dyes Obtained from Minerals

Dyes made by minerals, coloured clays and earth oxides. For instance, Ochre, made from iron ore, is one of the oldest pigments and has been in utilizing since pre-historic times.

Categories of Natural Dyes 

Table: Categories of Natural Dyes

Colours

Chemical

Classifications

Common Names

Yellow and Brown

Flavone Dyes

Weld,  Quercitron,

Fustic, Osage,

Chamomile,  Tesu,

Dolu, Marigold, Cutch

Yellow

Iso-quinoline Dyes

Barberry

Orange-Yellow

Chromene Dyes

Kamala

Brown  and  Purple-

Grey

Naphthoquinone Dyes

Henna,  Walnut,

Alkanet, Pitti

Red

Anthraquinone Dyes

Lac, Cochineal,

Madder (Majithro)

Purple and Black

Benzophyrone Dyes

Logwood

Blue

Indigoid Dyes

Indigo

Neutrals

Vegetable Tannins: gallotannins,

ellagitannins and

catechol tannins

Wattle,  Myrobalan, Pomegranate, Sumach,

Chestnut, Eucalyptus

Natural dyeing

Beautiful bright colours can be attained through dyeing by natural dyes. Dyes can be gathered from nature or we can utilize dyestuff which will provide we any colour under the rainbow.

Some natural dyeing materials

a. Alkanet Root (Alkania tinctoria): This will provide colours from bluish grey to soft burgundy. This plant grows as a weed when planted.

b. Annato Seed (Bixa Orellana): Will provide an orange shade, it is a good dye for cotton.

c. Brazilwood Dust (Caesalpania echinata): This dye will provide reds. Before using the dust, it is 1st exposed to the air and sprinkle through water and alcohol.

d. Cochineal (Dactylopius occurs): The little cochineal bug will provide the most colours when ground into a fine powder. Attainable colours are dark burgundy to bright red, soft lilac and pink.

e. Indigo Solution Natural (Saxony blue): Produces a bright blue and is extremely easy to utilize, similar to a chemical dye. All of the dye will be absorbed in the fiber. It isn't very good to dye cotton or other vegetable fibers.

f. Red Sandalwood (Pterocarpus): This dye is beautiful for blending. It produces lovely browns and act as good shade combinations for doll hair.

g. Madderroot (Rubia tinctorum): Is available in 2 forms: root or dust. Colour ranges from red to red-brown and oranges. It dyes cotton well.

h. Loqwood Concentrate (Hematoxylon campechianum): Expected colours anywhere from magenta's and brown to purples and pink. A mordant is absolutely required. The concentrated powder will give more bluish colours. It dyes cotton well.

i. Osage Orange Dust (Maclura pomifer): 2 different colours can be attained; bright yellow and gold.

Mordants for Natural Dyeing

Mordants are required to set the colour when using natural dyes. Different mordants will provide different consequences:

(a) Alum: (AlK2SO4; Aluminum Potassium Sulfate): This is the most widely utilized mordant. Be careful not to utilize too much through wool, otherwise we will obtain a sticky feeling that doesn't come out.

(b) Copper: (CuSO4; Copper Sulfate): This mordant is used to bring out the greens in dyes. It will also darken the dye colours, similar to using tin, but is less harsh.

(c) Chrome: (K2Cr2O7; Potassium Dichromate): Chrome brightens dye colours and is more commonly used with wool and mohair than with any other fiber. Chrome should not be inhaled and gloves should be worn while working with chrome.  Left over mordant water should be disposed of at a chemical waste disposal site and treated as hazardous waste.

(d) Iron:  (Fe2SO4; Ferrous Sulfate): Dulls and darkens dye colours. Using too much will make the fiber brittle.

(e) Glaubersalt:  (Na2SO4; Sodium Sulfate): Used in natural dyes to level out the bath. Also use in chemical dye.

(f) Spectralite: (Thiourea Dioxide): This is a reducing agent for indigo dyeing.

(g) Tara Powder: (Caesalpinia spinosa): Tara Powder is a natural tannin product. It is needed for darker colours on cotton, linen and hemp.

(h) Tartaric Acid: A must for cochineal. This mordant will expand the cochineal colours.

(i) Tin: (SnCl2; Stannous Chloride): Tin will provide extra bright colours to reds, oranges and yellows on protein fibers. Using too much will make wool and silk brittle. To avoid this we can add a pinch of tin at the end of the dying time with fiber that was premordanted with alum.  Tin isn't generally utilized through cellulose fibers.

(j) Calcium Carbonate (CaCO3): Is to be utilized by indigo powder for the saxon blue colour. It can as well be utilized to lower the acidity of a dye bath.

Making Natural Dyes from Plant Source

There is a simple experiment requires to obtain dyes from plant materials.

(a) Gathering plant material for dyeing:  Blossoms should be in full bloom, berries ripe and nuts mature. Never gather more than 2/3 of a stand of anything in the wild when gathering plant stuff for dying.

(b) To make the dye solution: Chop plant material into small pieces and place in a pot. It is most appropriate to double the amount of water being added to the plant materials. Bring to a boil, and then simmer for about an hour. For a stronger shade, permit substance to soak in the dye overnight.

Natural dyeing process

(a) Equipment: The water we utilize for dyeing should be soft. Most tap water is as well hard, and we should add a softener to it. Rain water might be an ideal option. The subsequent items are helpful for dyeing;  stainless  steel  pot,  strainer,  stirrer,  wooden  spoon, measuring  utensils,  as cups  and  spoons,  kitchen  scale  and rubber gloves.

(b) Wool Preparation: When working by raw wool fleece, we must 1st scour the wool to eliminate the oil from the fiber. For 1lb of wool: fill 3-4 gallons of water in a pot through detergent. Put the wool in and slowly simmer for 45 minutes. Cool, then rinse.

(c) Mordant Directions: Dissolve the mordant in a tiny amount of hot water. Add 4-5 more gallons of water, enough to cover 1lb of wool, and heat to luke warm.  Add the wool and simmer 45 minutes to 1 1/2 hours. Cool and rinse.

Dyeing process  

(i) Place wet wool in luke warm dye bath and slowly rise to a simmer.

(ii) Dyes from flowers, fruits, and tender leaves: simmer 30 minutes - 1 hour

Dyes from tough leaves, roots, nut hulls, and bark: simmer 1 minute - 2 hours

(iv) Cool and clean until the rinse water is clear.

(v) Never agitate the wool or it will felt. Lift and turn it gently in plenty of water.

(vi) Never shock by extreme changes in water temperature

(vii) Don't wring or twist - squeeze gently to eliminate excess water. It isn't needed to cover the pot when simmer in, unless you are using chrome which is light sensitive.

(ix) Dye entire amount of wool needed for project in one bath

(x) Add white vinegar (1/4 cup per gallon) to rinse water to assist soften the wool.

Fibre dyeing

Natural dyes can dye fibres in 3 chief forms:

(a) Direct dyes can colour fibres with no other fixing agents, often after easy extraction from plant substance. Such comprise extremely fast colours, these as walnut and bark browns, and as well dye by extremely poor fastness, these as Saffron (Crocus sativus), Safflor (Carthamus tinctorum) and Pomegranite rinds.

(b) Adjective dyes colour fibres only in combination by a mordant. The most significant mordants are metal salts (aluminum, iron, copper) and tannins. The ancient dyeing traditions of Egypt, India, China and Central America all incorporated utilize of such minerals. The practices of mordant-dyeing worldwide are remarkably similar and these discoveries as the fixative properties of metal salts were made via many early peoples.

(c) Indigo dyes are a exclusive form of natural dye that utilize particular procedures. Complicated dye extraction using fermentation and even more complicated dyeing practices were extended in pre-historic cultures of Europe, Asia, Africa and the Americas, wherever indigo-bearing plants have been found in nature. Indigo blues can be fairly permanent when correctly applied.

Dyeing Process of Leather

Dyeing Leather substrate is an uphill task. As leather has myriad of structural differences, grooves, knurls, and folds along by other sorts of imperfections. Hence for achieving the target of a level and uniform dyeing, the dyer requires to be experienced, and have a thorough knowledge of the dyeing procedures, properties and the auxiliaries that require to be utilized. Leather dyeing is usually done through 2 processes. Drum dyeing and Rub dyeing, by Drum dyeing being predominant. In the procedure of drum dyeing, the application of dyestuffs to the leather is done via immersing the leather in drums. The drum is then tumbled. This tumbling permits the leather to be completely penetrated via the dyes. The ultimate aim of drum dyeing is getting the wished colour that appears level and uniform throughout the skins. The leather colourants that are employed is dominated via the acid dyes that accounts for nearly 90% of the market, followed via metal complex dyes and, cationic dyes to some extent. The dyes are applied either on the grain or suede side.

Some dyeing patterns

(i) Raw fibres are usually dyed via the dipping procedure. They are positioned in a perforated metal cylinder, which is dipped into a vat full of dye.

(ii) Velour cloth and furs are often hand-dyed. The dye is applied by a brush that has been dipped in a dye solution.

(iii) Batik is an ancient technique of pertaining coloured dyes to fabrics, generally cotton and silk. It originates in Java and now widely utilized throughout the world.

(iv) Tie- dyeing, a hand-dyeing technique often practiced as a craft, can be employed to generate multi-coloured patterns.

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