enhancement of materials-1.5

Question 1

what are the three stages of dyeing?

Answer 1

1. immersing the fabric in soluble dyestuff
2. the dye attaching itself to the fabric through absorption or a reaction with the fibres
3. fixing the dye so the colour remains in the fabric

Question 2

large scale dyeing is done in dye baths called…

Answer 2

vats

Question 3

what is vat dyeing?

Answer 3

large scale dyeing

Question 4

how is vat dyeing done?

Answer 4

1. the vats are filled with dye liquor ( a mixture of dyestuff, water and added chemicals to help the dye attach itself to the fabric) and the fabric is dyed in batches
2. the fabric is continuously moved in the vat to ensure an even dye distribution/penetration and the dye attaches itself evenly
3. excess dye is removed and the fabric is washed with detergents and dried- if the fabric is not washed after dyeing, the fabric may develop faults such as losing colour when washed or streaking of the colour.
4. washing helps avoid later colour loss

Question 5

discharge dye…

Answer 5

removes colour from a dyed fabric using a colour destroying deactivator that removes colour from a fabric

Question 6

resist dyeing…

Answer 6

creates patterns by preventing colour from going onto certain areas of the fabric using a resist such as a string or elastics etc

Question 7

what are the four types of resist dyeing?

Answer 7

-batik
- tie-dye
-shibori
-tritik

Question 8

what is the process of tie-dye and what is one negative of this process?

Answer 8

involves wrapping, folding and twisting areas on a fabric and tying tightly which makes it difficult for the dye to be absorbed here. Multi-coloured patterns can be achieved by refolding/tying/wrapping the fabric and dyeing with another colour.

the only negative is that tie-dye is unpredictable- if you have mixed colours, you may not know what colour the fabric will be when washed and dried, or how the final pattern would have turned out. This can therefore be an expensive process when used in commercial manufacture as some fabrics may not have turned out accurately and will need to be wasted.

Question 9

what type of fabrics does tie-dye work well on?

Answer 9

natural fibres

Question 10

what is the process of batik dyeing?

Answer 10

patterns are applied by hand using melted wax or rice paste using a brush or tjanting tool. once the wax has dried, the applied areas prevent the dye from going onto these areas of the fabric. the fabric can be submerged in a dye bath or painted with different coloured dyes. After this, the wax or paste can be removed.

Question 11

what is the process of tritik?

Answer 11

fine, running stitches can be applied to a fabric, then pulled tight before dye is applied. After dyeing, stitching is removed, revealing a pattern.

Question 12

what are the advantages of tritik?

Answer 12

-good for intricate designs
-works well on natural fibres

Question 13

what is the process of shibori?

Answer 13

Japanese method of folding or tying fabrics, then applying a combination of heat and dyes, or chemicals. When fabric is dried, the ties are removed. Works on all types of fibres and fabrics.

Question 14

what are the 5 different stages in which dye can be applied?

Answer 14

-dope/spin dyeing
-stock dyeing
-yarn dyeing
-piece/fabric dyeing
-garment dyeing

Question 15

what is dope/spin dyeing?

Answer 15

where man made fibres are coloured before fibre extrusion in the melt or dry spinning process- the dye is added to the spinning solution which makes it part of the fibre. this method results in having textiles with good light and wash fastness

Question 16

what are the advantages of dope/spin dyeing?

Answer 16

-gives the finished fibres excellent light and wash fastness

Question 17

what is stock dyeing and what is the benefit of this?

Answer 17

-fibres, also known as stock, can be dyed in their loose and raw form before they are spun or twisted into a yarn. The benefit of this is that if the dyeing is uneven, the fibres are not wasted as the uneveness will be removed by the blending processes when converting the fibres into yarn

Question 18

what is yarn dyeing and what is the benefit of this?

Answer 18

the yarn is dyed before construction into woven or knitted fabrics. this gives good fastness to washing and wearing and so they are almost always used to make high quality shirts and suit fabrics.

Question 19

what does dyed yarn enable for?

Answer 19

for the production of multi-coloured, patterned fabrics such as stripes, checks and jacquards- different coloured weft and warp yarns can be used in the weaving process and alternate between twill, satin and plain weave to create elaborate patterns

Question 20

what is the one disadvantage of dyeing yarn?

Answer 20

-dyeing at this early of a stage commits the manufacturer to a fabric colour

Question 21

what is piece/fabric dyeing?

Answer 21

manufacturers can hold greige fabric (undyed, woven or knitted fabric) and dye it as needed to respond to changing fashion styles and colour trends. This is the most commonly used stage as it enables just-in time processing

Question 22

what does griege/loomstate mean?

Answer 22

terms used for a fabric in it’s natural state as it comes from the weaving loom or knitting machine

Question 23

what is garment dyeing?

Answer 23

finished garments can be dyed. A colour can be chosen at this very last stage, enabling retailers and manufacturers to react rapidly to market trends and consumer demand.

Question 24

what is degradation and what are the three types of degradation?

Answer 24

The gradual breakdown of a dye, leading to colour loss in a product

1. fading- the colour is faded into the atmosphere
2. crocking- the colour is lost through abrasion
3. bleeding- the colour is lost in water

Question 25

what are the 7 different ways colour in a fabric can degrade?

Answer 25

-washing -bleaching -dry cleaning -perspiration -toiletries and cosmetics -light -rubbing (crocking)

Question 26

how can washing degrade colour in a fabric?

Answer 26

dye can 'bleed' from a fabric when wet- this is an important aspect that manufacturers need to consider when dyeing- will the final garment be laundered continuously?

Question 27

how can bleaching degrade colour in a fabric?

Answer 27

chlorine bleach can remove colour from most fabrics so dyes used in swimwear need to be resistant to chlorine

Question 28

how can dry cleaning degrade colour in a fabric?

Answer 28

the solvents used in dry cleaning can cause some dyes to fade

Question 29

how can perspiration degrade colour in a fabric?

Answer 29

a reaction to acids in sweat causes colour loss in localised areas such as under the arms

Question 30

how can toiletries and cosmetics degrade colour in a fabric?

Answer 30

chemicals used in deodorants and perfumes can cause discolouration

Question 31

how can light degrade colour in a fabric and what is an example of a product that needs to be resistant against light degradation?

Answer 31

dye degrades and fades if repeatedly exposed to strong, bright sun or artificial light. products such as curtains need to resist the bleaching effects of the sun

Question 32

how can rubbing (crocking) degrade colour in a fabric?

Answer 32

abrasion can cause dye loss or colour transfer when dry, dyed fabric rubs against a lighter coloured fabric

Question 33

how do manufacturers keep consumer demand in mind during dyeing processes?

Answer 33

by dyeing fabric at the last stage possible and using just-in-time (JIT) stock control systems gives manufacturers the opportunity to respond quickly to changes in consumer demand -piece fabrics can be kept in their greige state (natural colour state) and dyed as needed -simple-shaped garments can be manufactured and kept undyed then dyed to order - manufacturers can employ colour forecast analysers that interpret the moods and preferences of consumers in particular seasons and make accurate predictions about colours that will be popular at least a year in advance to allow for the manufacturing process. These trends are often shown at trade fairs such as premiere vision, which is held twice-yearly in Paris.

Question 34

how are printed designs different to fabric dyeing?

Answer 34

1. printed designs don't fully penetrate through a fabric, giving it an identifiable right and wrong side

Question 35

what are the main advantages of printing over dyeing?

Answer 35

-more colours can be used -complicated designs can be produced -is it better for the environment as less water is used -the methods of printing are more varied and can give greater decorative effects -typically less costly than dyeing

Question 36

what are the three steps for preparing a fabric for printing and why do these steps need to be done?

Answer 36

when a woven or knitted fabric is removed from the weaving loom or knitting machine, it is not yet ready to be dyed or printed on straight away . At this point, it is referred to as being in it's 'greige' state, and is often a natural creamy colour. It goes through three steps before it is ready to be printed on: 1. desizing 2.scouring 3.bleaching

Question 37

what is the process of desizing?

Answer 37

-the removal of 'size'- a water-soluble substance known as starch that is added to warp yarns to strength them before weaving so they can withstand the constant movements of the weaving loom. It needs to be removed from the fabric before printing as it can inhibit the absorption of dye or print medium. Starch is typically easily removed using water as it is soluble in water so washing can remove it easily

Question 38

what is the process of scouring?

Answer 38

-the removal of natural or machine impurities such as greases and oils that act as a barrier to dye or print medium absorption- greases and oils often repel water. For example, cotton fabrics are scoured by boiling them in caustic soda solution. This method would not be appropriate for wool as it is easily damaged by heat and alkalis, instead they are moved through warm detergents to remove fatty deposits in the fibres (such as lanolin, a greasy natural substance found on wool which makes it water repellent- it is excreted through the skin of the sheep)

Question 39

what is the process of bleaching?

Answer 39

making the fabric evenly white before colour is added to ensure that the dye is even across the fabric. synthetic fibres are naturally white so do not require bleaching, however natural fibres such as cotton have a natural creamy off-white appearance.

Question 40

how is discharge printing done?

Answer 40

the fabric is dyed and then discharge paste is screen printed onto dyed fabric. the chemicals in the paste destroys the original dye to produce a pattern or printed design.

Question 41

what are the advantages of discharge printing?

Answer 41

-intricate patterns can be produced -suitable for designs with large areas of background colour -suitable for large print runs

Question 42

what are the disadvantages of discharge printing?

Answer 42

-two production stages are involved -discharge paste is expensive

Question 43

how is block printing by hand done?

Answer 43

- a design is cut into a wooden block. printing paste is applied to the block. The block is pressed firmly onto the fabric leaving a repeating pattern

Question 44

what are the advantages of block by hand printing?

Answer 44

-can be used on any fabrics and any fabric size -sustainable process as blocks can be reused -gives an ethnic craft aesthetic

Question 45

what are the disadvantages of block by hand printing?

Answer 45

-time consuming, particularly if multiple colours are being used, as each individual colour needs to be dried before using another to avoid bleeding or colours unintentially mixing/blending -expensive -accurate positioning is essential -a block is needed for each colour -only suitable for small scale runs rather than commercially produced products

Question 46

how is stencil printing by hand done?

Answer 46

gaps are cut into acetate or card to create a pattern. the stencil is then positioned onto the fabric and printing paste is sponged or brushed through the cut areas, or in some cases a printing paste/fabric paint in a spray diffuser.

Question 47

what are the advantages of stencil printing by hand?

Answer 47

-stencils can be cut by hand or using a laser cutter -stencils can be reused -stencilled patterns can entirely cover or enhance small areas of fabrics

Question 48

what are the disadvantages of stencil printing by hand?

Answer 48

-time consuming -suitable for simple designs with limited colours -stencils need to be used with care as the sections are connected with narrow 'bridges'

Question 49

how is rotary screen printing done?

Answer 49

the screen in this form of screen printing is individual mesh rollers which rotate and print one colour and part of the design in turn. The rollers then rotate as the fabric travels below on a conveyor belt. an internal squeegee which is positioned in the centre of the roller has printing paste automatically fed to it through a pipe attachment, and then forces the printing paste through open mesh areas onto the fabric. Each roller prints one colour across the width of the fabric. The designs are usually prepared using CAD software and a screen is prepared for each colour in the design.

Question 50

what are the rollers in rotary screen printing made from?

Answer 50

stainless steel mesh or photochemically on woven nylon

Question 51

what are the advantages of rotary screen printing?

Answer 51

-it is the most commercially viable way of printing large quantities of fabric- incredibly fast and economical and faster than flatbed screen printing in some cases -suited to designs that have pattern repeats -can produce complex designs with five or more colours -CAD is used to prepare the design and set up a screen (roller) for each colour in the design -knitted fabrics can be printed on as this doesn't stretch the fabric

Question 52

what are the disadvantages of rotary screen printing?

Answer 52

-long set up time -not suitable for JIT manufacturing -the circumference of the rollers dictates the length of the pattern repeat -only suitable for high-volume print runs -the initial investment cost for machinery is high

Question 53

how is the screen in flat bed screen printing made?

Answer 53

flatbed screen printing involves stretching a finely woven mesh fabric over a metal or wooden frame to form a screen. Photochemicals known as 'Emulsion' is used to coat the front and back of the screen - the design is drawn on a separate piece of paper and placed behind the stencil. The screen is then exposed to UV light- the photochemical that was pasted onto the screen is sensitive to UV light, and when exposed to UV light, the chemical becomes insoluble (cannot disolve) in those areas that are not blocked off, . when the screen is washed, the unexposed chemical is removed and the print paste is able to pass through the mesh. a separate screen is needed for each colour in the design

Question 54

how is flat bed screen printing done after the screen has been created?

Answer 54

a conveyor belt moves and stops the fabric under printing screens. The screens are lowered, automatic squeegees push printing paste through 'open' areas of the screens. the screens are raised and the fabric moves on using the conveyor belt to receive another colour

Question 55

what are the advantages of flatbed screen printing?

Answer 55

-accurate and relatively fast -used for high volume print runs -good for small-width fabrics -can be used on a wider range of fabrics as the number of squeegee passes can be increased -investment cost is lower than rotary screen printing machines

Question 56

what are the disadvantages of flatbed screen printing?

Answer 56

-slower than rotary screen printing -takes up more factory floor space -not suitable for JIT production -not cost-effective for small orders -better suited to designs with few colours

Question 57

how is transfer/sublimation printing done?

Answer 57

CAD generates the design, which should be the same length and width as the fabric that will be printed on. Long rolls of sublimation paper and inks are used to print the design. the printed paper and white fabric are held together in a heat press with the printed paper facing down onto the fabric- it is also important to consider that the design should therefore be printed onto the special sublimation paper inverted. High temperatures cause the printed dyes to turn into vapour, transfering under pressure and bonding with the fabric.

Question 58

what are the advantages of transfer/sublimation printing?

Answer 58

-quick set up and turnaround time reduces costs -no colour or design constraints -colour adjustments can easily be made using CAD -good colour fastness as the dye bonds with the fabric -fabric retains a soft handle -similar to ironing transfers onto fabric -low cost technique -suited to short print runs -design can be changed quickly and easily to meet with consumer demand

Question 59

what are the disadvantages of transfer/sublimation printing?

Answer 59

-only effective on fabrics with 50% or more synthetic fibre content -slower than screen printing methods -slightly creased fabric ruins the transfer print -a range of processes are required to set up a print run

Question 60

how is digital printing done?

Answer 60

CAD generates the design. The pattern is sent to an ink jet printer fitted with direct dye printing cartridges. The pattern is printed directly onto the fabric or simple garment, the design is then set into place using heat or steam

Question 61

what are the advantages of digital printing?

Answer 61

-no colour or design constraints- no limit on the amount of colours that can be used -colour changes are quick to do -patterns do not have to repeat -works on most fabrics -suitable for JIT production as the design goes straight from the computer software to the printer- short lead times and no minimum print run. New designs can be produced very quickly and used on any fabric, so manufacturers are not dependant on stock fabric. -rapid turnaround of samples -no minimum print run

Question 62

what are the disadvantages of digital printing?

Answer 62

-expensive -suitable for small print runs -the size of the printer and printable area determines the width of the fabric that can be used -not an economic method for high volume production

Question 63

what must you consider before dyeing?

Answer 63

1. sustainability 2. colours- trends, meanings etc 3.fitness for purpose- it's fastness to bleaching, perspiration etc 4. The type of dye to use- acid, direct, disperse 5. whether you want to use computer systems

Question 64

what can computer systems do for dyeing?

Answer 64

1. reduces faults/flaws 2. increased accuracy + consistency 3. reduced costs (labour) 4. time efficient 5. can create dye for small or large scale dye runs + printing

Question 65

What are the three types of hand printing methods?

Answer 65

-block printing -stenciling -screen printing

Question 66

what are the key differences between modern printing methods and hand printing methods?

Answer 66

-hand printing methods are a lot less efficient and are labour intensive- meaning it is usually a lot more expensive -hand printing methods are limited to a couple of colours- particularly if you are using block printing -modern printing methods can use CAD which reduces labour costs and human error -hand printing methods are only suitable for small scale production runs whilst modern printing methods can be suitable for large scale production -hand printing methods are more likely to have human error mistakes -complex designs can be created using CAD with multiple different colours -modern printing methods support consumer demand- allows for quick editing of designs to meet consumer demands

Question 67

what is dye fastness/colour fastness?

Answer 67

the ability for a fibre or fabric to retain dye during the manufacturing process an during the use and care of the product by the consumer.

Question 68

why are there three steps involved in making woven and knitted fabrics suitable for printing?

Answer 68

-fibres, especially natural ones have impurities in them, for example fats, waxes and salts and other impurities would have been picked up during the processing of the fibre for example oil and dirt from the machine. - sometimes starch is added to strengthen yarns before weaving- this has to be removed before the fabric can be dyed or finished, otherwise the colour or finish will not attach itself evenly to the fabric

Question 69

how are cotton fibres bleached?

Answer 69

used controlled amounts of hypochlorite bleach or hydrogen peroxide

Question 70

why is wool never bleached using chlorine and what can it be bleached with instead?

Answer 70

Wool is never bleached using chlorine and often left in its natural state as well as the bleach can damage the scales along the fibre. It can be bleached using hydrogen peroxide instead or sulphur dioxide gas.

Question 71

what are the two types of screen printing?

Answer 71

-Rotary screen printing -flatbed screen printing