Textiles Part 35

_Questions_

1. What is meant by yarn-dyed fabric?

2. What is meant by piece-dyed fabric?

3. How may the two be distinguished?

=Experiment 25--Test to Distinguish Dyed from Printed Fabrics=

Apparatus: Knife-blade.

Materials: Cotton fabrics.

Reference: _Textiles_, page 65.

Printed fabrics may be distinguished from dyed by observing the back side of the cloth, and noting whether or not the pattern on the face of the cloth penetrates through to the back, or only the outline shows. In case the figure or pattern is on both sides of the fabric, it may be distinguished from the dyed by taking one thread of the suspected sample, and by the means of a knife-blade attempting to sc.r.a.pe off the coloring on the surface of the thread. If the dyestuff has penetrated into the interior of the thread, it is _not_ printed.

Generally speaking, printed fabrics are known from dyed fabrics by the fact that the former have the design printed on the face of the cloth.

This is called _direct printing_. The best dyed fabrics are obtained by dyeing in what is called a _jig_, and the whole fabric is saturated with color. Most, if not all the cloths which you see in the retail dry goods stores which are in plain colors are dyed in the jig. Some of the cheaper qualities of dyed fabrics are padded in a mangle, but there has been a very small quant.i.ty of these goods on the market for many years.

Printed fabrics may be made as fast as dyed fabrics; it all depends upon the process by which the goods are converted. Within the past few years great headway has been made in dyeing with what are termed _vat_ colors. Indanthrene is a vat color and a great many mills have used this cla.s.s of dye successfully in dyeing plain shades. This is what would be termed a _fast_ color in every sense of the word. There are a number of dyestuff makers in Europe who put vat colors on the market, but they all call them by different names. Vat colors have been used with success in printing during the past year or two, especially on shirting fabrics, and these colors are fast to both light and washing.

Most direct colors used for printing or dyeing are equally fast to light and washing, but of course they will not stand the test as well as the vat colors mentioned above.

The essential qualities of a good printed fabric are its ability to withstand exposure to light and washing. In printing, of course, a greater variety of desirable styles can be obtained than by dyeing, in fact there are certain popular lines of goods now on the market the effect of the designs of which cannot be obtained in any other way than by printing. At the same time, although the field in designing for dyed fabrics is limited, some very handsome effects can be obtained.

It will not be many years before a large proportion of the printed and dyed fabrics put on the market, both foreign and domestic, will be in the vat colors which, as stated above, are very fast. Even at the present time there are many mills that are using this cla.s.s of colors entirely, especially the mills which manufacture woven fabrics.

_Questions_

1. In printed fabrics is the pattern clearly discernible on the back of the cloth?

2. If the fabric is printed on both sides, how may this fact be proved?

3. What is the difference between printed and dyed fabrics?

=Experiment 26--Bleaching by Sulphur Dioxide=

Apparatus: A quart bottle.

Material: Sulphur, worsted or silk fabric.

Bleaching powder cannot be used in bleaching animal fibers such as woolen and silk fabrics. It injures the fibers and at the same time leaves them yellow.

Animal fibers are best bleached by immersing in an aqueous solution of sulphurous acid or exposing them to fumes of burning sulphur.

Wet a piece of dyed worsted or silk fabric and hang it in a quart bottle containing fumes of burning sulphur.[26] The fumes of burning sulphur have an affinity for coloring matter--dyestuff. The fumes (called sulphur dioxide) do not in most cases destroy the coloring matter as chlorine does, but simply combine with it to form colorless compounds which can be destroyed. The color can be restored by exposing the bleached fabric to dilute sulphuric acid.

_Questions_

1. Why is it necessary that the fabric be moist in order to be bleached by sulphur dioxide fumes?

2. What becomes of the coloring matter?

=Experiment 27--Bleaching by Bleaching Powder=

Apparatus: Porcelain dish.

Material: Piece of calico.

Reference: _Textiles_, page 148.

_Directions_

Place a quarter of an ounce of bleaching powder in a quart bottle containing a pint of water.[27] Then place a piece of calico in the water containing the bleaching powder. What is the effect on the calico? Then remove cloth to another bottle filled with dilute hydrochloric or dilute sulphuric acid. What is the effect on the color? Then wash the whitened cloth thoroughly in water.

Why is it necessary in practice to pa.s.s cotton fabrics through two baths in bleaching? What is contained in the first bath? in the second bath?

=Experiment 30--Determining Style of Weave=

Apparatus: Pick gla.s.s.

Materials: Different fabrics.

References: _Textiles_, pages 56-58, etc.

Examine different samples of cloth and cla.s.sify them according to the seven standards given on pages 56-58, etc.

=Experiment 31--Determining the Size of Yarn=

Apparatus: Yard stick.

Materials: Sample of cotton, woolen, and worsted yarns.

References: _Textiles_, pages 49, 51, 52.

As yarns used in the manufacture of fabrics are of all degrees of thickness, it became necessary to adopt some method of measuring this thickness. For this purpose yarns are numbered, so that when the number is known an idea of the size of the yarn may be gained. It would seem advisable to number yarns of all kinds according to one fixed standard, yet unfortunately this is not done. The methods of counting yarns are many and varied. The usual method is to estimate the yarn number by taking the number of hands of a definite length which make up some given weight. Thus in the worsted yarn, No. 1 is a yarn that has 560 yards to a pound. No. 2 worsted yarn has two times 560 yards to a pound. How many yards in No. 12 worsted yarn? How many yards in No. 20 cotton yarn?

=Experiment 32--Test for Twist in Yarn=

Apparatus: Test dial.

Material: Piece of yarn.

References: _Textiles_, pages 131-132.

As the amount of twist in yarn determines its strength, it is necessary to know the amount of twist per inch in given yarn. The strength increases up to a certain limit. When this limit is reached, increased twist does not make the thread any stronger. We may also have twist and strength at the expense of bulk. The test consists in finding out the number of turns per inch, and this is done by an arrangement where a certain length of yarn is stretched between two points on a twisting machine and the twist taken out. The number of turns required to take the twist completely out are registered on a dial at the side of the apparatus.

Poor cotton that goes into coa.r.s.e goods cannot be spun as fine as the finer cotton. The shorter the cotton the more twist is required to spin it, and the more twist that is put into the yarn, the less will be the yardage. Whereas on the finer and longer cotton there will be less twist put into it, and the yarn will be much stronger. Find the twist in different kinds of yarn.