In a former chapter the intricately delicate structure of the knitted loops was described, and the causes of some of the minor defects of stitch were outlined when the utmost importance of a regular feed of yarn to the needles was emphasized. Another important series of defects in knitted articles are directly traceable to faults in the stitch-forming parts of the machine, such as the sinkers and needles, and many imperfections spring from faulty condition or adjustment of these parts. The needle is perhaps the most delicate part of the frame and constant attention has to be given to these if perfect knitting has to be produced. Large firms find it to their advantage to engage an operative for this special work alone, he inspects all frames and his trained eye can soon detect the slightest fault of needle alignment and he replaces faulty needles by casting new ones. The pliaring of needles, as it is called, is an important part of the work of a modern knitting factory, and care to these machine parts is at once reflected in the quality of the fabric produced on the frames. A constant source of trouble in knitting is the beard or spring of the needle, and if these are not properly hardened or tempered their period of service is much shortened, because the beard soon develops faulty action and refuses to spring back into its former position after the removal of the presser. If the beard has lost its spring the new yarn cannot be pushed properly underneath, a common defect being for the stitch to be halved, one portion of the thread going under and the other half over the spring of the needle. These split stitches cause small puckerings in the texture which seriously affect its market value, and when the yarn is split in this fashion the stitch at this point has only half its strength, the thread gets broken and a hole is caused in the fabric. Another defect in the needle occurs when the beard is working out of its true position in a vertical direction, the beard in place of going straight into the groove lands a little to the right or the left when it catches the yarn as it is drawn forward.

Sinker and Needle Lines.—Sinker and needle lines are formed vertically in the fabric and are due to needles and sinkers being out of alignment in relation to their neighbours. If the needle is raised above or depressed below the normal level of the needle line, or if it is not in the exact central position in relation to the needle at each side a defect will be formed, which will show vertically in the fabric. A diagrammatic view of this kind of fabric blemish is given in Fig. 58 where the line is marked A and is formed by a vertical series of loops of larger curves than those around. The sinker line and the needle line are alike in general appearance except that the sinker line affects the sinker wales and the needle lines the needle rows. The needle at A has been pushed a little to the left so that more than normal spacing occurs, and this causes an extra length of yarn to be served to the stitch at this point. It might be more correct to say that this extra length is supplied at the expense of the neighbouring loops at B and C which are seen to be smaller than the normal. The needle in moving to the left out of the true central position between its neighbours enlarges the draw at one point, but makes a corresponding contraction of the stitch at B where the needle has to be content with a shorter piece of the yarn. This is the basic reason why these lines are so conspicuous, the regular spacing of the needles is departed from and there is always a large-size loop side by side with a shorter and more contracted stitch. The sinker line may also be caused the same way and has the same general appearance; if the sinker is not working in its true central position between two needles there is a variation in the length of loop which shows a line as before. In the case of the sinker, the lines may be produced from another cause, and that is the wearing of the sinker at its throat, the part employed for pushing the yarn between the frame needles. This wearing of the sinker throat will tend to reduce the size of the loop at that point, because it will not be able to take a sufficient length of loop when pushed forward. Similar defects are caused if the sinker is rough, and another blemish is known as "cutting," where the yarn is totally or partially cut through as the sinkers push the yarn between the needles. Cutting may be due to the push of the sinker being too great, or it may be caused by yarn which is not strong enough to stand the strain of loop sinking.

Other Defects.—A very common defect which will prove disastrous if not remedied is given at Fig. 59, known popularly as a "Jacob's Ladder." This will be noted to be due to a stitch running down in a vertical direction and caused in the first place by a breaking of the thread. Once this severance has taken place the stitch loses its supports and unravels as long as the least strain is imposed upon it. The method of repairing this is to take the last perfect stitch in the run and link it up with the slack thread of the course immediately above until the whole fabric has been restored, the top stitch being secured suitably to prevent a repetition of the unravelling. This linking of the stitch can be done very rapidly by an experienced hand with the aid of a turning hook which is indispensable for repairing all defects in the knitted texture. If the loops get severed by a cross cut the process of repairing the break is much more complicated and requires greater skill to rehabilitate. The cut loops have to be unravelled to give a perfect row of stitches on which to base the repair, and the missing courses have to be entirely rebuilt by the needle of the operative. In reconstructing those missing stitches, they have to be formed as nearly as possible of the same size as will correspond to the fabric gauge, and it requires years of experience for a worker to acquire the ability to reconstruct the fabric in such a way that the rent will be imperceptible. In some hosiery districts the saleable quality of their products is much reduced owing to faulty repairing of cross imperfections, in many cases the practice prevails of simply drawing the stitches tightly together and securing them. To repair a large hole in a knitted structure the usual way is to patch by cutting the broken part out in the form of a square running directly crosswise with the loops and directly vertical with the wales of the fabric. The patch is made from a piece of fabric identical in gauge and texture with the ground fabric, and the stitches are knitted to each other crosswise at the top and bottom of the square, a perfect union being possible; vertically the patch is seamed and joined to the ground fabric by a row of ordinary sewing which is drawn round to the back of the garment and which, if skilfully performed, gives but little indication of the blemish. A worker skilled in this branch of repairing knitted fabrics proves of the greatest value to any knitting mill, and her efforts result in the salving of large numbers of expensive garments which might otherwise have to be disposed of at sacrificial prices.

Slurgalling.—This term is applied to several defects in knitted fabrics which are the bane of hosiery manufacturing and belong to the type of imperfections which it is extremely difficult to repair, whilst in many cases it is not a practical possibility. A few stitches of this kind of imperfection are given herewith in Fig. 60, which is a diagrammatic enlargement of the wrong side of the plain knitted loop where the defect is shown plainly by means of the black coloured stitches appearing crosswise in the fabric. It consists of a tightening of the loops due to a momentary increase of the tension of the thread during knitting; the stitches become constricted and at once injure the general amenity of the fabric. Even minor variations in yarn tension will cause these crosswise defects in the cloth, and they are so minute in their formation that it is almost impossible to repair them. If any irregularity creeps into the tensioning of the thread as the carrier is moving from right to left as compared with its motion from left to right, then the variation in the size of the loops may be perceptible at alternate courses and occur right across the fabric. Small obstructions on the yarn surface such as knots, burrs or slubs, will produce a momentary catch on the aperture of the thread-carrier and cause this cross constriction of loops; a rough carrier nose is a fruitful source of trouble if any grooves are being worn in the instrument. In some machines a worn slurcock may be the cause of such irregularities.

Stitches of Variable Symmetry.—These defects are illustrated in various forms in Fig. 61, which gives a diagrammatic view of the chief variations which are met with in single stitch formation in the knitted texture. During knitting the yarn usually forms itself into curved loops, but various conditions have to be met if this curving has to be perfect. Should the knitting yarn be lacking in yielding property curves will not eventuate, but will be replaced by various distorted formations. Very often the mechanical structure of the yarn makes it impossible for the thread to fall out in nicely-shaped curves, this taking place when the constituent fibres are tightly arranged in the yarn or when they are composed of long fibres drawn with meticulous precision in parallel order side by side. A much more suitable thread is worked from shorter materials which gives a freer scope of direction. This renders the thread less rigid and makes it more amenable to loop formation, whilst the beneficial effects of lubrication or damping of dry yarn have already been referred to. Several typical examples of these deficiencies are illustrated in Fig. 61 by means of the stitches marked 1 to 4. Stitches 1 and 2 show a mal-formation of loop due to a straightening of the yarn, the fibres are too long and do not yield in loop formation. With hard yarns which are thick for the gauge of the frame, these straightened loops may occur six or eight together and have the effect of tightening the fabric at that point, at other times they take up a direction leaning to the right or the left which greatly impoverishes the goods. The more usual type of mal-formation is given in loops 3 and 4 where the stitch, unable to content itself with the length of yarn allotted to it, takes up an enlarged area. These are termed "pinholes," and when scattered all over a fabric seriously undermine its value.

Manufacturers are often baffled by a plain fabric issuing from the frame of the rotary type using bearded needles which shows an effect like 2 and 1 rib, that is, there is a minute opening after every second stitch which, by its general appearance, resembles 2 and 1 rib, the space giving the impression of the open part formed by the vertical row of loops which go to the back of the texture. Wherever this is detected attention should be given to the dividing of the loops in the machine. In stitch formation for an average bearded needle machine the loops are first sunk over alternate needles, and thereafter equalized or divided over all the needles. When the equalization is not accurately performed, as is the case when the divider sinkers are not pushed sufficiently between the needle or are pushed too far, then the ribbed effect will be produced. Another common defect occurs at the selvedge consisting of a variable tension of the end loops, some being large and others constricted. This may be due to the yarn having too much play at the edge, so that the end two sinkers are permitted to draw more than their quota of yarn for stitch formation, which makes the edge raw and unsightly and gives trouble in seaming when the quality of the seam is variable owing to the different size of loop. The remedy for this imperfection lies in an adjustment of the snappers which exercise a drag on the thread just when the end sinkers show a tendency to take more than their share of yarn.