TESTING MATERIALS

New Zealand Herald, Volume LXXI, Issue 21861, 25 July 1934, Page 5

TESTING MATERIALS

gIMPLE METHODS APPLIED HINTS ON DYEING BY Ol'lt DRESS .SPECIALIST / Having learned something of the Characteristics of each of the live chief fibres, it is now a simple matter to apply a scries of tests to any material to ascertain whether it is a pure and reliable fabric and suitable for the purpose. It is always advisable before purchasing the piece to obtain a small sample of the material under consideration, and put it to these tests at home, as it is not possible to do some of them in the shop. The first lest is the burning test. Take separately some of the warp threads which run lengthwise of the material and some iilling threads which run widtlnvi.se, as sometimes there is a mixture or an adulterant present. Carefully untwist each of these threads to discover if two or more yarns have been used'to make the thread, and if so divide the thread into its constituent yarns. Apply a lighted match to one end of the yarn, note how it burns, then blow out the flame and smell the fumes given otl by the smouldering thread. Material that flames readily and continues burning when the match has been' removed, is vegetable in origin and is cotton, linen or rayon. It also burns to a grey ash, giving off a smell of burnt paper or faintly like vinegar. Celanese also burns like this, but the edges curi up leaving black globules/' Material that flames with difficulty, and ceases doing so when the match is removed, and gives off a smell of burnt feathers, is either silk or wool. Wool leaves black bubbly globules, and so does silk if it is pure. If it is weighted silk, the material turns black and retains its, original shape, not forming beads. This is a sure test for weighting. To distinguish between silk and rayon, then, burn the threads and note the result. ,/ Linen and Cotton To distinguish between linen and cotton is not so easy, but the following two tests can be easily applied. Place a drop of water on the material when it is lying flat. If it fairly quickly is absorbed, leaving an opaque spot on the cloth, it is linen, if it is cotton, the absorptio'n is much slower owing to the tiny hairs on the surface, and the material is not rendered opaque. Hence the value of linen for household use. Again, if the thread -n question is well wetted and single fibres pulled out, using the thumb and index finger, it will be ;ioticed that if the loose end be toward the observer, these loose fibres begin to rotate, lr the rotation is in a clockwise direction, the thread is linen; if it is an irregular movement, it is cotton. Should these two tests not be convincing the ultimate one is to place a fibre under the microscope, when linen appears like bamboo rods and cotton like ribbon. Generally speaking, linen material has a tough, leathery feel and is cold and smooth, whereas cotton is dull, harsh and lifeless when crushed in the hand. Weighting in cotton, linen or wool can be detected by rubbing a sample between the hands, when a white or coloured powder dropping out indicates sizing in cotton or linen. The material will then be noticed to be much thinner. Willi wool, fluff and small lumps of wool may fall out, this "fulling" having been pressed into the material in its finishing processes to disguise a thin weave. Weave and Shrinkage The next consideration is the weave. Hold a strip of the material firmly by the thumb and finger of each hand and pull backwards and forwards. A looselywoven material will show signs of strain and pull apart. This indicates a weakness in the weave. Again, if such

a material be pulled perfectly straight it may burst, indicating inferior yarns. •, oavos winch have long threads floaton the surface, such as satins, are not so durable as plain weaves, for 'P"K threads are apt to catch and pull. ISotiee, then, whether the pattern is made by such long threads, which not give long service. Ihe weave oi the material may also o its design, as 111 the case of many 1 '• criukly crepes at present in \ogue. It, is wise to take a sample of tins and subject it to washing and iron•ng to fiaul whether its crinkly condition is permanent or removable by laundering. All materials shrink. The finishing processes employed with the different fabrics determine their width and length, the final pressing sometimes reducing their width in order to oUain greater length. When these fabrics are made wet then it stands to reason they return to their original shape. That accounts for much of the shrinkage, and therefore it is wise to wash materials before making them up in order to avoid the possibility of shrinkage afterwards. This shrinkage cannot be satisfactorily tested in a small piece Many people consider woollen material should bo dampened and pressed before making up, to shrink it. But it seems hardly likely that th<> amount of shrinkage obtained by the inefficient equipment in the home can produce any marked difference in a material which has already been shrunk in the mills. Dyeing and Printing "Fast dyes" aro often untruthfully so-called, and so when contemplating buying a coloured material it is wisest to put the fabric ro some tests. Take a sample and rub it with a damp white cloth. The colour may come off, in which case such a material would not be suitable for wearing purposes. Then wash a sample, expose it to sunlight and iron it, noting whether any of these processes change its colour. Jf the material is likely to be exposed to much sunlight leave the sample in the sun for several days, then note its colour and test its strength, for some dyes have a harmful effect on the fabric on being exposed to sunlight. It is possible that some dyes are fast to sunlight and not to washing; these then would be suitable for, say, curtain material. Therefore, subject the sample to whatever treatment it is most likely to have when made up.

Fabrics can be dyed either in the yarn or after they are woven. Those dyed in the yarn are most likely to be permanent. This can be determined by withdrawing a thread from tho material. If it is evenly coloured it has been dyed in the yarn; if it has white streaks along it, it has been dyed after being woven and the dye has not penetrated deeply. Printing of fabrics is done by several methods, one being "by discharge," when the whole material is dyed one colour, and then run through a • machine which prints on to it an acid which discharges or removes the colour, forming a design. Such discharging acid often weakens the fabric in those places' and such materials should be subjected to laundering and exposed to sunshine to test their strength.