Friday, January 29, 2010

Discharge Printing

Discharge Printing is also called Extract Printing. This is a method of applying a design to dyed fabric by printing a color-destroying agent, such as chlorine or hydrosulfite, to bleach out a white or light pattern on the darker coloured ground. In color-discharge printing, a dye impervious to the bleaching agent is combined with it, producing a colored design instead of white on the dyed ground.
Discharge printing has been around for decades. But only in the past 7-8 years screen printers in the industry have recognized it seriously. In the early years of discharge printing, the finished discharge print needed to be steamed during the drying process. This discouraged the use of discharge systems in the finished garment arena. The newly developed discharge ink systems are chemically reactive and dont need to be steam-neutralized. This advancement opened the door to discharge printing for the average screen printer.
Discharge printing has the ability to make bright, opaque colors on dark fabrics with a soft hand. Years ago the idea of opaque colors on dark fabrics and soft hand couldnt co-exist.
Successful light-on-dark printing with plastisol relies on increased pigment loads, fillers and other additives to block out the color of the garment. Discharge inks modify the garment color by removing the garment color and replacing it with the new ink color. In simple terms, the discharge ink "bleaches" out the dye in the garment, thus allowing the pigment in the ink to absorb into the shirt fibers.
The real magic of discharge printing can be witnessed when printing four-color process on black 100% cotton shirts. The print before curing appears very transparent. One can barely see the print until the garment exits the oven chamber, where the results can be quite remarkable: bright, vivid colors with a soft hand.
The graphics on the casino gaming tables are printed with discharge inks to avoid the interference of the printed line with the roll of the dice. If the ink on these tables were printed with plastisol, the ink film (because it is a surface print) would change the speed and direction of the dice, thus changing the way the dice land. Discharge ink, on the other hand, provides a dyed-in-the-fabric result, keeping the playing surface smooth.
The decrease in the production time is the biggest bonus of all. The fact that you can skip flash curing completely saves hours of production time and eliminates registration problems between the designs colors and the white printer under base used in normal printing on blacks.
However, flash curing can be used in conjunction with discharge printing when printing discharge as an under base.
Cleaner and more transparent inks can also be printed onto dark garments with the help of discharge additives. Early discharge additives were designed only for water base inks, but plastisol additives are available.
Characteristics that indicate a garment will work with discharge ink
• The garment has to be made of natural fibers (100% cotton)
• The dye used in the garment must be dischargeable. The best results are achieved with garments that are 100% cotton and dyed with a reactive dye.
• The garment should not have been over dyed (when fabric is re-dyed to another color). This often happens because of a shortage of a certain fabric color or, in many cases, because quality control rejected the fabric color. These rejected colors are then over dyed with a black dye, which will bring nightmares to life when trying to use discharge inks. The discharge ink might discharge the black dye - only to reveal a phantom color underneath.
Always test your garment to see if it is suitable for discharge printing. If you are a major printer doing large-volume printing, be aware that the shirts you order from the mill are tracked by lot numbers and it is possible that a completely different dye may be used from one lot to the next. Let your sales representative know that you are doing discharge printing and mention in writing that you need a dischargeable garment.
Points to be noted
• Do not to overlap your separations if you want to print clean spot colors. Butt-to-butt separations are ideal for most discharge printing.
• Work with a negative background and allow the dark background of the garment to show through. If you choose to overlap the color separations, overlap the primary colors - red, blue and yellow - to achieve secondary and tertiary colors within the design.
• To create the screen for under-basing with discharge ink, sandwich all the color separations together (make a contact sheet or a mask) to allow the discharge ink to be printed under all subsequent colors. (Suitable plastisols can be printed over clear discharge bases. Consult your ink manufacturer for compatibility with plastisol.)
• Discharge printing is frequently used for all-over prints because of its soft hand.



The kalamkari, handpainted cloths of Sri Kalahasti, Andra Pradesh, works of art drawn entirely by hand, were originally created predominantly for the temples as narrative murals.
These murals tell the stories of the great Hindu epics in picture form. Earlier this century, Christian missionaries commissioned artists to create murals telling the story of Christ.
In addition to the epic murals, the Tree of Life theme is very popular and comes in many forms. Artists are also branching out and using the medium for their purpose.
Kalamkari is an exquisite ancient craft of painted and printed fabrics. It derives its name from Kalam meaning Pen, and Kari meaning work, literally Pen-work. It includes hand painting as well as block printing with vegetable dyes. Kalamkari art has evolved through trial and error over the last 3000 years. Techniques of craftsmanship in Kalamkari were handed down within the families from generation to generation.
The Kalamkari art of painting undergoes a laborious, slow process of resist - dyeing and hand printing. Many stages have to be undergone before the final results are achieved. Unlike other styles of painting, Kalamkari painting demands a lot of treatment before and after the painting is completed on the cotton fabric. Depending on the treatment of cloth, or quality of the mordant, the colors change accordingly. Every step from soaking of the cloth, to sketching the outlines to washing and drying the cloth, is done carefully and correctly.
The world over, people are turning away from dangerous chemical dyes. The harmless, naturally dyed fabrics is used for Kalamkari paintings. The artists believe in using natural dyes, extracted from bark, flower and root. One would be stunned to know that the colour red is obtained by using the Indian madder root, yellow from the pomegranate seed or even mango bark, and black from myrobalam fruit. No chemical dyes are used is producing kalamkari colours!
The process used for both schools of Kalamkari painting is more or less the same. The only major difference is that Srikalahasti paintings depend entirely on the brush-like pen whereas the Masulipatnam style uses block-printing procedures. The process done in Srikalahasti is more tedious. The cloth is treated and washed twice, and is painted with alum for two to three times.
• Whitening the cloth by immersing in a solution of goat or cow dung and letting it dry in the Sun for a few days.
• The cloth is then treated in Myrobalan solution. Ripe fruits are used in Masulipatnam, raw ones in Srikalahasti. Milk is then added to the solution to prevent the colour from spreading in the next step.
• Then iron acetate solution is filled in, either for solid spaces or as outlines, with a brush-pen in Srikalahasti, and wooden blocks in Masulipatnam.
• All the areas meant to be red are painted or printed over with the alum solution as a mordant. Mordant is a substance that fixes the natural dye on the material.
• After applying alum, the cloth is kept for at least 24 hours. Then the excess mordant is removed by washing the cloth under flowing water.
• The dyeing is done for the red colour by boiling with the red coloring materials.
• All the portions that are not to be blue are covered with wax.
• The waxed cloth is immersed in indigo solution. In Srikalahasti, the blue is painted with the kalam. Then the wax is removed by boiling the cloth in water.
• The yellow is painted on to produce yellow and green.
• The cloth is finally washed again and dried before the final colours emerge.

Thursday, January 28, 2010

Sanganeri & Block printing

History of Block Printing

Records show that as far back as the 12th century, several centers in the south, on the western and eastern coasts of India became renowned for their excellent printed cotton. On the southeastern coast the brush or kalam (pen) was used, and the resist applied by the same method. In the medieval age printing and dyeing of cottons was specially developed in Rajasthan. In Gujarat the use of wooden blocks for printing was more common. Tents were created from printed fabrics and became a necessary part of royal processions. The seasons largely influenced the integration of the highly creative processes of weaving, spinning, dyeing and printing. Festivals also dictated this activity. Block printing is a special form of printing first developed in China. The earliest known example with an actual date is a copy of the Diamond Sutra from 868 A.D (currently in the British Museum), though the practice of block printing is probably about two thousand years old
Trade in cotton cloth is said to have existed between India and Babylon from Buddha's time. Printed and woven cloths traveled to Indonesia, Malaya and the Far East. In the 17th century, Surat was established as a prominent center for export of painted and printed calicos, covering an extensive range in quality. Cheaper printed cloth came from Ahmedabad and other centers, and strangely enough Sanganer was not such a famous center for printing as it is today.
Block Printing in Gujarat
In Gujarat, this form of hand Printing has been practiced and perpetuated by the Paithapur families. They make intricate blocks, and print their textiles using the mud resist-Printing method. These prints are called Sodagiri (trader) prints. In Kutch, the popular patterns are black and red designs of birds, animals, and dancing girls. The saris of Ahmedabad and Baroda have large mango patterns against a red or blue background. The other well known centers for block Printing in Gujarat are Bhavnagar, Vasna, Rajkot, Jamnagar, Jetpur and Porbandar. Dhamadka a village in Gujarat has many printers using mostly madder root for printing red color, rusty iron solution for black color and indigo for blue color. These fabrics are known as Ajrakh. The designs made by block printing are geometric. Many states have block-printing workshops using chemical dyes. However there are only small pockets of areas still using natural dyeing with age-old recipes and local plant material.
Block Printing in Rajasthan
From Gujarat, the art of block Printing spread to Rajasthan. Here colorful prints of birds, animals, human figures, gods and goddesses are popular. The important centers are Jaipur, Bangru, Sanganer,Pali and Barmer.
Sanganer is famous for its Calico printed bed covers, quilts and saris. In form of hand Printing are Calico Printing, the outlines are first printed, and then the color is filled in. Bold patterns and colors are popular. They are printed repeatedly in diagonal rows. Doo Rookhi Printing is also famous here. In this technique, artists print on both sides of the cloth.
Bagru is famous for its Syahi-Begar prints and Dabu prints. The former are designs in a combination of black and yellow ochre or cream. The latter are prints in which portions are hidden from the dye by applying a resist paste.
Barmer is known for its prints of red chilies with blue-black outlines, surrounded by flower-laden trees. The other famous prints are of horses, camels, peacocks and lions, called Sikar and Shekahawat prints.
Block Printing in Punjab
The block Printing from Punjab is not as famous as its Rajasthani counterpart, but is still merit worthy. It was the art of a group of textile workers called Chhimba . The designs were usually floral and geometrical. Today, traditional designs have been displaced, and vegetable dyes have been replaced by chemical ones. The colors are light and pastel. The motifs are usually mangoes, peacocks and nets.
Block Printings of Andhra Pradesh
In Andhra Pradesh, the block Printing method is applied in the creation of the exquisite Kalamkari Printing . The two major centers of Kalamkari art are Sri Kalahasti and Masulipatnam. Masuliputnam in Andhra Pradesh is the main centre of block printing where the fabric is known as Kalamkari. The cloth used generally is mill made cotton, which is first bleached with cow dung and placed in the sun. The next step is to soak the cloth in a mixture of Myrobalan and milk. The Myrobalan contains tannic acid and acts as a mordant helping the dyestuffs to bond with the fibre. The buffalo milk, having high fat content, helps prevent the dye from running. Then the black outline is printed using a solution made with rusty iron soaked in sugar water and bran for several weeks. When the solution comes in contact with the myrobalan it turns black. The next step is printing on another mordant, alum.
This bonds the red dye, Madder Root, after boiling, to the areas that receive the alum. These steps continue until all colours have been printed or brushed on. It is crucial to have a good water supply for washing after printing. It takes weeks to complete all these steps.
Block Printing is also practiced in Madhya Pradesh, Uttar Pradesh and Maharashtra.

The first step in block printing is the production of the original document. This is laid on a large, smooth wooden block and fixed into place, reversed. Next, craftsmen of various skill levels, ranging from master carvers for the fine work to less talented artisans for cheaper blocks or less important sections, carve the original painted, drawn or written image into the block of wood. The block can now be covered with ink and used in a press to create duplicates of the original.
In some ways block printing is superior to cast type or moveable type -- for a language such as Chinese which has a very broad character set, block prints are much cheaper to produce for the initial run. The process also allows greater artistic freedom, such as the easy inclusion of pictures and diagrams. However, printing blocks are not very durable, and deteriorate very rapidly with use, requiring constant replacement that limits the possibility of large-scale print runs. Printing blocks can, however, be made from a variety of materials such as wood, linoleum, rubber, or even potatoes.
Method and equipments used in Hand Block printing
This process, though considered by some to be the most artistic, is the earliest, simplest and slowest of all methods of printing.
The blocks may be made of box, lime, holly, sycamore, plane or pear wood, the latter three being most generally employed. They vary in size considerably, but must always be between two and three inches thick, otherwise they are liable to warping, which is additionally guarded against by backing the wood chosen with two or more pieces of cheaper wood, such as deal or pine. The several pieces or blocks are tongued and grooved to fit each other, and are then securely glued together, under pressure, into one solid block with the grain of each alternate piece running in a different direction.
The block, being planed quite smooth and perfectly flat, next has the design drawn upon, or transferred to it. This latter is effected by rubbing off, upon its flat surface, a tracing in lampblack and oil, of the outlines of the masses of the design. The portions to be left in relief are then tinted, between their outlines, an ammoniacal carmine or magenta, for the purpose of distinguishing them from those portions that have to be cut away. As a separate block is required for each distinct color in the design, a separate tracing must be made of each and transferred (or put on as it a termed) to its own special block.
Having thus received a tracing of the pattern the block is thoroughly damped and kept in this condition by being covered with wet cloths during the whole process of cutting. The blockcutter commences by carving out the wood around the heavier masses first, leaving the finer and more delicate work until the last so as to avoid any risk of injuring it during the cutting of the coarser parts. When large masses of color occur in a pattern, the corresponding parts on the block are usually cut in outline, the object being filled in between the outlines with felt, which not only absorbs the color better, but gives a much more even impression than it is possible to obtain with a large surface of wood. When finished, the block presents the appearance of flat relief carving, the design standing out like letterpress type.
Fine details are very difficult to cut in wood, and, even when successfully cut, wear down very rapidly or break off in printing. They are therefore almost invariably built up in strips of brass or copper, bent to shape and driven edgewise into the flat surface of the block. This method is known as coppering, and by its means many delicate little forms, such as stars, rosettes and fine spots can be printed, which would otherwise be quite impossible to produce by hand or machine block printing.
Frequently, too, the process of coppering is used for the purpose of making a mold, from which an entire block can be made and duplicated as often as desired, by casting. In this case the metal strips are driven to a predetermined depth into the face of a piece of lime-wood cut across the grain, and, when the whole design is completed in this way, the block is placed, metal face downwards in a tray of molten type-metal or solder, which transmits sufficient heat to the inserted portions of the strips of copper to enable them to carbonize the wood immediately in contact with them and, at the same time, firmly attaches itself to the outstanding portions. When cold a slight tap with a hammer on the back of the limewood block easily detaches the cake of the type-metal or alloy and along with it, of course, the strips of copper to which it is firmly soldered, leaving a matrix, or mold, in wood of the original design. The casting is made in an alloy of low melting-point, anti, after cooling, is filed or ground until all its projections are of the same height and perfectly smooth, after which it is screwed on to a wooden support and is ready for printing. Similar molds are also made by burning out the lines of the pattern with a red-hot steel punch, capable of being raised or lowered at will, and under which the block is moved about by hand along the lines of the pattern.
In addition to the engraved block, a printing table and color sieve are required. The table consists of a stout framework of wood or iron supporting a thick slab of stone varying in size according to the width of cloth to be printed. Over the stone table top a thick piece of woolen printers blanket is tightly stretched to supply the elasticity necessary to give the block every chance of making a good impression on the cloth. At one end, the table is provided with a couple of iron brackets to carry the roll of cloth to be printed and, at the other, a series of guide rollers, extending to the ceiling, are arranged for the purpose of suspending and drying the newly printed goods. The color sieve consists of a tub (known as the swimming tub) half filled with starch paste, On the surface of which floats a frame covered at the bottom with a tightly stretched piece Of mackintosh or oiled calico. On this the color sieve proper, a frame similar to, the last but covered with fine woolen cloth, is placed, and forms when in position a sort of elastic color trough over the bottom of which the color is spread evenly with a brush.
The modus operandi of printing is as follows: The printer commences by drawing a length of cloth, from the roll, over the table, and marks it with a piece of colored chalk arid a ruler to indicate where the first impression of the block is to be applied.
He then applies his block in two different directions to the color on the sieve and finally presses it firmly and steadily on the cloth, ensuring a good impression by striking it smartly on the back with a wooden mallet. The second impression is made in the same way, the printer taking care to see that it fits exactly to the first, a point which he can make sure of by means of the pins with which the blocks are provided at each corner and which are arranged in such a way that when those at the right side or at the top of the block fall upon those at the left side or the bottom of the previous impression the two printings join up exactly and continue the pattern without a break. Each succeeding impression is made in precisely the same manner until the length of cloth on the table is fully printed. When this is done it is wound over the drying rollers, thus bringing forward a fresh length to be treated similarly.
If the pattern contains several colors the cloth is usually first printed throughout with one, then dried, re-wound and printed with the second, the same operations being repeated until all the colors are printed.
Many modifications of block printing have been tried from time to time, but of these only two tobying and rainbowing are of any practical value. The object of tobey printing is to print the several colors of a multicolor pattern at one operation and for this purpose a block with the whole of the pattern cut upon it, and a specially constructed color sieve are employed. The sieve consists of a thick block of wood, on one side of which a series of compartments are hollowed out, corresponding roughly in shape, size and position to the various objects cut on the block. The tops of the dividing walls of these compartments are then coated with melted pitch, and a piece of fine woolen cloth is stretched over the whole and pressed well down on the pitch so as to adhere firmly to the top of each wall; finally a piece of string soaked in pitch is cemented over the woolen cloth along the lines of the dividing walls, and after boring a hole through the bottom of each compartment the sieve is ready for use. In operation each compartment is filled with its special color through a pipe connecting it with a color box situated at the side of the sieve and a little above it, so as to exert just sufficient pressure on the color to force it gently through the woolen cloth, but not enough to cause it to overflow its proper limits, formed by the pitch-soaked string boundary lines.
The block is then carefully pressed on the sieve, and, as the different parts of its pattern fall on different parts of the sieve, each takes up a certain color that it transfers to the cloth in the usual way. By this method of tobying from two to six colors may be printed at one operation, but it is obvious that it is only applicable to patterns where the different colored objects are placed at some little distance apart, and that, therefore, it is of but limited application.
Block printing by hand is a slow process~ it is, however, capable of yielding highly artistic results, some of which are unobtainable by any other means, and it is, therefore, still largely practiced for the highest class of work in certain styles.

Thickening Agents

The thickening agents in most general use as vehicles in printing, are starch, flour, gum arabic, gum senegal and gum tragacanth, British gum or dextrine and albumen.
With the exception of albumen all these are made into pastes, or dissolved, by boiling in double or jacketed pans, between the inner and outer casings of which either steam or water may be made to circulate, for boiling and cooling purposes. Mechanical agitators are also fitted in these pans to mix the various ingredients together, and to prevent the formation of lumps by keeping the contents thoroughly stirred up during the whole time they are being boiled and cooled.
Starch paste
This is made by mixing 15 lb of wheat starch with a little cold water to a smooth creamy paste; a little olive oil is then added and sufficient water to bring the whole up to 10 gallons. The mixture is then thickened by being boiled for about an hour and, after cooling, is ready for use.
Starch is the most extensively used of all the thickenings. It is applicable to all but strongly alkaline or strongly acid colors. With the former it thickens up to a stiff unworkable jelly, while mineral acids or acid salts convert it into dextrine, thus diminishing its thickening power. Acetic and formic acids have no action on it even at the boil.
Flour paste is made in a similar way to starch paste. At the present time it is rarely used for anything but the thickening of aluminum and iron mordants, for which it is eminently adapted.
Gum arabic and gum senegal are both very old thickenings, but their expense prevents them from being used for any but pale delicate tints. They are especially useful thickenings for the light ground colors of soft muslins and sateens on account of the property they possess of dissolving completely out of the fibers of the cloth in the washing process after printing. Starch and artificial gums always leave the cloth somewhat harsh in feel unless they are treated specially, and are moreover incapable of yielding the beautifully clear and perfectly even tints resulting from the use of natural gums. Very dark colors cannot well be obtained with gum senegal or gum arabic thickenings; they come away too much in washing, the gum apparently preventing them from combining fully with the fibers. Stock solutions of these two gums are usually made by dissolving 6 or 8 lb of either in one gallon of water, either by boiling or in the cold by standing.
British gum or dextrine is prepared by heating starch. It varies considerably in composition sometimes being only slightly roasted and consequently only partly converted into dextrine, and at other times being highly torrefied, and almost completely soluble in cold water and very dark in color. Its thickening power decreases and its gummy nature increases as the temperature at which it is roasted is raised. The lighter colored gums or dextrines will make a good thickening with from 2 to 3 lb of gum to one gallon of water, but the darkest and most highly calcined require from 6 to lb per gallon to give a substantial paste. Between these limits all qualities are obtainable. The darkest qualities are very useful for strongly acid colors, and with the exception of gum senegal, are the best for strongly alkaline colors and discharges.
Like the natural gums, neither light nor dark British gums penetrate into the fiber of the cloth so deeply as pure starch or flour, and are therefore unsuitable for very dark strong colors.
Gum tragacanth, or Dragon, is one of the most indispensable thickening agents possessed by the textile printer. It may be mixed in any proportion with starch or flour and is equally useful for pigment colors and mordant colors. When added to starch paste it increases its penetrative power, adds to its softness without diminishing its thickness, makes it easier to wash Out of the fabric and produces much more level colors than starch paste alone. Used by itself it is suitable for printing all kinds of dark grounds on goods that are required to retain their soft clothy feel. A tragacanth mucilage may be made either by allowing it to stand a day or two in contact with cold water or by soaking it for twenty-four hours in warm water and then boiling it up until it is perfectly smooth and homogeneous. If boiled under pressure it gives a very fine, smooth mucilage (not a solution proper), much thinner than if made in the cold.

Surface active agents

Surface active agents or surfactants have a distinct molecular structure that gives rise to their molecular properties. [extra background]
Soaps such as sodium oleate are examples of a class of molecules called surfactants. The name "surfactant" comes from somebody who we don't think would spell very well - it actually stands for SURFace ACTive AgeNT. Both detergents and soaps are classed as surfactants.
Surfactants are characterised by the essential features that we saw in sodium oleate. A surfactant molecule has a hydrophilic (water-loving) head and a long hydrophobic (water-hating or oil-loving) tail. For this reason, we often describe surfactants is being amphiphilic molecules - they love everything.

Surfactants are said to have a "head" and a "tail". The head is hydrophilic which means that it is water loving, and it is generally depicted as a circle. The tail is generally a long hydrocarbon chain and is hydrophobic, which means water-hating (therefore oil-loving). The tail may be depicted either as a straight line or a wavy tail.
Properties of Surfactants
The molecular structure of surfactants means that they have unusual properties, leading to both widespread and highly specialised applications. The properties of surfactants fall into two broad categories: adsorption and self-assembly.
Adsorption is the tendency for a surfactant molecule to collect as an interface. Adsorption is very different to absorption (don't get them confused!):
the taking up of a gas or liquid at the surface of another substance, usually a solid (for example, activated charcoal adsorbs gases). It involves molecular attraction at the surface.
the taking up of one substance by another, such as a liquid by a solid (ink by blotting paper) or a gas by liquid (oxygen dissolving in water).
The adsorption properties of surfactants mean that surfactant molecules are usually found at the interface between an oil phase and a water phase or a water phase and an air phase. This molecular property leads to the macroscopic properties of wetting, foaming, detergency and emulsion formation.

Surfactant molecules tend to adsorb to the surface of oil droplets. The hydrophilic heads stick out into the water phase, while the hydrophobic tails happily stick into the oil phase.

Self-assembly is the tendency for surfactant molecules to organise themselves into extended structures in water. This includes the formation of micelles, bilayers and liquid crystals. These structures are formed by when the hydrophobic tails of the surfactants cluster together, forming small aggregates such as micelles, or large layer structures (bilayers) which are similar to a cell wall.
These properties make surfactants very interesting study, and are areas of current research.

Surfactants can aggregate to form micelles. Forming a micelle allows the hydrophobic tails to get out of the water but still allows the hydrophilic heads to stay in the water. There is usually between a few dozen to a couple of hundred surfactant molecules in a micelle.

Surfactants also aggregate to form extended structures in water, such as the surfactant bilayer depicted here.