Intarsia (Figures 10.2 and 10.3) is a special method of producing designs in knitted loops that form self-contained areas of pure colours. Unequalled colour definition
is achieved, with a large number of colours and no adverse effect on the physical properties of the structure such as reduction of extensibility.
Careful positioning of the yarn carriers and control of the extent of traverse of each from course to course determines the design and integration of the coloured areas into a cohesively-knitted structure. Such a cohesive structure is achieved by slight overlap of adjoining areas and the intermeshing of loops in each wale. As well as plain and 1 x 1 rib, other stitches such as purl or cable may be utilised.
A design row of intarsia is divided into adjoining blocks of contiguous wales. Each block of needles knits a separate coloured area (field), for which it is exclusively supplied with its own particular yarn (Fig. 10.2). The yarn then passes to the course above and does not float across the backs of needle loops. If there are further blocks of needles in the design row requiring the same colour, each will be supplied by a separate yarn.
The knitting action and supply of yarn for intarsia is from left-to-right at one course, and right-to-left at the next. This is the normal reciprocating movement found on all V-bed flat machines and straight bar frames. On circular, single-cylinder sock machines, it is necessary to oscillate the cylinder (similarly to heel knitting) instead of continuously revolving it.
Traditionally, intarsia was skilfully knitted by hand, laying the yarns into the hooks of each block of adjacent needles as they are cammed outwards, on hand-operated stationary needle bed machines such as the circular Griswold type sock machine or the flat bed Dubied model 00 machine.
High-quality woollen Argyle tartan socks and sweaters can be knitted, consisting of diamond-shaped designs crossed diagonally by one wale wide stripes termed overchecks.
Only on a hand-manipulated flat machine with hand-feeding of the yarn can a pure join of adjoining areas be achieved. As the edge yarn of an area rises to the next course, it crosses over and links to the edge yarn of the adjacent colour area.
Most automatic methods of knitting intarsia entail some way of overlapping (encroachment) of adjoining areas into each other, towards the right at one course and towards the left at the next. A slight saw-tooth effect across one, two, or more wales is thus produced at the join, which should be kept to a minimum, and the plating of knitted or tuck loops can be employed. Argyle socks can be knitted automatically with plated overchecks.
Intarsia designs for full-fashioned sweaters have generally been balanced geometrical shapes because of the screw spindle control of the carrier stops. However, intarsia patterning as an optional extra on electronic V-bed flat machines is becoming increasingly sophisticated (Fig. 10.3), with precise yarn positioning, needle selection and carrier traversing that may be controlled electronically.
Although intarsia ensures that expensive yarns are fully utilised on the surface of the design, it is only generally suitable for geometric type designs (although they no longer need to be symmetrical) and not for figure designs in small areas. It is a comparatively slow, expensive, specialised technique that is subject to the whims of fashion.
Plating is widely used for single jersey, plush, open-work, float and interlock fleecy. However, with the exception of embroidery motif plating, the use of coloured yarns to produce plated designs has diminished in weft knitting. Plating requires great precision and offers limited colour choice with poor definition compared with the improved facilities offered by jacquard knit and miss needle selection of coloured stitches.
In reverse plating, two yarns (usually of contrasting colour) are caused to change over positions at the needle head by controlled movement of specially-shaped sinkers or yarn feed guides.
In sectional plating (straight bar frames), the ground yarn knits continuously across the full width whilst the plating carrier tubes, set lower into the needles, supply yarn in a reciprocating movement to a particular group of needles, so that the colour shows on the face.
The one major advance in pattern plating coloured yarns has occurred in weft embroidery motif plating on electronically-controlled, single-cylinder hosiery machines knitting so-called 'computer socks'. The main yarn is a fine, undyed filament nylon, which is continuously knitted throughout the sock. At each feed there is a group of coloured bulked yarns. A selected yarn is fed, in a plating relationship with the main yarn, to one or a group of adjacent needles according to the required design. The next adjacent needle(s) will receive a different coloured yarn, selected from the same group of yarns.
All the needles will thus receive a plated bulked yarn of some colour, whether they are knitting the motif or the ground colour. The designs appear to be pure colour intarsia because the main yarn is fine and is hidden by the plated, coloured bulked yarns. There are no floating threads on the inside of the sock because the yarn is cut and trapped when not in use. Care must be taken to ensure that the pattern threads are securely retained in the fabric.
Simple motif embroidery designs using warp threads have, for many years, been wrap-knitted on the side panels of double-cylinder half-hose. The technique is slow and less popular than weft embroidery patterning.
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