Preparing the Clay:
The main raw material used for ceramic pottery is clay procured from varies places like Kerala, Rajasthan, Delhi, Bikaner, Bihar, and Ahmedabad in the country. Different raw materials like.
The main raw material used in ceramic pottery is clay mixed with varies materials like quartz, potash feldspar, china clay and ball clay procured from Jaipur, Ahmedabad and Bikaner, kundan clay from Kerala, Rajmahal clay from Bihar, and fire clay from Delhi (Ref: RITES 1992 report). All these raw materials are mixed in a defined ratio (trade secret) and grinded in a Ball-mill equipment for around 10 hours to get homogenous mix of clay dough and further placed between pace filter (pressed between metal plate and canvas cloth) to remove the excess water content and clay disc of size around 1.5 feet diameter is the output of this process. Clay discs are again passed through Pug-mill equipment for pugging process to get super fine clay dough. Archimedes screw in pug-mill pushes the clay through, horizontal and vertical motion. Two types of clay material is produced, liquid clay used in molding and clay dough.
Clay Molding Process:
Molding process is generally done for bigger products like vases and pots. Mold of required article with the product cavity is prepared using Plaster of Paris (POP). Clay is mixed in a liquid solution with no lumps as material. Clay solution is poured into the mold till the solution fills the cavity in the mold. Mold box is shaken/rotated/tilted gently to avoid air bubbles and excess clay liquid solution is dispensed out, when the wall of the article reaches the required thickness. Molded product is elected with the help of a blade from the rim and other surface of the mold after settling time. Products kept to dry in room temperature for a day.
Jigger and Jolly Process:
In this process the products are made with an equipment called Jigger and jolly, contains a die in jigger and a cavity in jolly to shape the clay. Jigger equipment consists of a movable handle (up & down) which holds the die and a base (rotatable) to place clay dough whereas jolly equipment is same as jigger equipment but the base is to hold the cavity shaped bowl. A thick dough of clay with more elasticity is used in this process.
The holder (handle) is meant to hold different shapes of dies and fed against the clay dough kept on a rotating base to take the corresponding shape. Die on handle helps the clay dough to take shape by spreading on the base surface. Base plate come with a mechanism of replacing with another base plate on a base which helps to mass produce. Product is removed from the base and kept to settle to remove moisture on the base. Further it is taken from the base and kept to dry in room temperature (diffused sunlight). For products like coffee mug, cup and handle are made separately and fasten.
Dried products are subjected to semi-finish process to improve the surface finish by sanding with sand paper and un-even surfaces and parting lines. Cracks developed during the molding process also closed/filled with clay and allowed to dry followed by sanding. Sanded products are washed thoroughly using cotton cloth and plane water. Due to the addition of china clay as raw material, washed products turns half-white color before painting process.
Painting in ceramic pottery divided into 2 categories, Mughal art and normal painting with motifs on outer surface. Mughal art is painted with cobalt-blue color followed by a colorless lead glazing, whereas other category is drawing motifs like floral or geometric patterns drawn on the outer surface with oxide colors followed by a colorless lead glazing. Painting on a plain surface adds value to ceramic products.
Sticker ornamentation is another method of adding value to ceramic products like coffee mugs and crockeries, mainly used for advertising, better aesthetics and to display corporate identity. Decal labels can be produced in any range of style and color combination that is fused on a clay body surface (outside). Decals are manufactured separately with required patterns printed (ceramic ink made of color pigment+resin+plasticizer+solvent) on lacquer cover-coat protected with a removal standard size sticker paper, created digitally with the help of a computer (using software’s like Adobe Photoshop, CorelDraw etc.) and it can be screen printed as well to cut the cost. Decal label is dipped in plain water for 20-30 seconds (sometimes Acrylic spray is used to wet the decal labels) and fasten to the surface by peeling the sticker paper and allowed to dry for 1-2 hours followed by firing process. Lacquer cover burns away at around 800 degree centigrade leaving patterns fused to the surface where beautiful patterns on crockeries and mugs can be achieved. This type of sticker (Decal label) is called “Water-slide Decal paper”.
Glazing is a glossy layer fused to ceramic objects which serves to color, decorate, waterproof and to strengthen the underlying ceramic. Glazes can be transparent, opaque, translucent, glossy, semi- matte and matte finish. Glazes are made up of three basic elements, glass former, melter and binder.
Silica in the form of quartz, sand, flint and agate as glass former, lead/sodium or feldspar and calcium as melter and Alumina (combines well with silica to form a tough shock-resistant scratch proof surface) as binder. Three elements in the form of fine powder mixed with water to form a thin paste and Oxide color of required shade is added to the paste for plane articles and transparent glaze prepared for painted ceramic articles. Articles are dipped in the required solution according to the type of ceramic product and taken out immediately and dried in room temperature followed by firing process.
It’s a process done in a covered kiln. Earlier brick kiln were used but now a days it is replaced by gas or electric kiln with a temperature control technology which is easy for the artisans to operate and to avoid the number of damages. Firing in electric kiln helps to spread the heat uniformly in a given time. Around 20 minutes at a temperature of 1200 degrees is required to bake the articles. Firing at 1200 degrees more than a minute yield in glossy finish whereas firing close (1100 to 1150 degrees) to 1200 degrees would yield in matte or non-glare finish. Damaged pieces are reused and good pieces are sent for packing.