The art of kalai (kalhai or qalai) is the process of coating an alloy surface such as copper or brass by deposition of metal tin on it. [1] The word "kalai" is derived from Sanskrit word kalya lepa, which means "white wash or tin". [2] A cultural Sanskrit work by Keladi Basava called "Sivatattva Ratnakara" (1699) mentions "kalaya-lepa" in the chapter of cookery or "supashashtra" which means applying kalai on utensils. [2] People practicing the art of kalai are called Kalaiwala or Kalaigar. [3] Basically, Kalaigars or Kalaiwalas are community craftsmen. [4]
Vessels with kalai, both on its interior and exterior have been found in the excavations of Bramhapuri at Kolhapur, Maharashtra which adds to the archeological evidence of kalai art. [2] From this evidence, P K. Gode, who studied tin coating on metallic vessels in India, stated that the history of tin coating dates back to 1300 C.E. [2] The history of kalai is also recorded in “Parsibhashanushasana” of Vikaramasimha (before Samvat 1600 i.e. C.E. 1544) and also in the famous Ain- I -Akbari (C.E. 1590) by Abul Fazal. [2]
The copper vessels with kalai were used to store water and cook food earlier because of a spiritual belief that copper attracts and transmits a divine consciousness also called “Chaitanya”. [5] The spiritual approach to the use of copper vessels to store water is that copper and tin have Sattva-Raja (the basic component of creation/universe) component that is transferred to water. [5]
Earlier, copper and brass vessels were used because of their high conductivity. [6] High conductivity of copper vessels reduces the fuel cost. However, a chemical reaction between copper and oxygen called oxidization turns the copper vessels black. [7] Copper also reacts with the moisture in air and creates copper carbonate, which can be noticed as light green rust on the surface. Copper carbonate is poisonous and can make a person severely ill if it gets mixed with food. [7] The copper can get dissolved in water in trace amounts when the water is stored in copper vessels for a long period of time. The process is known as the “oligodynamic effect”. [6] Kalai protects from food poisoning and blackening of copper vessels by preventing direct contact of air with the copper or brass surface. Tin is also a good conductor of heat like copper, hence applying kalai does not result in loss of heat conductivity for the utensil.
The kalai is required to be done on the vessels approximately every two months. [6] Tin will melt if the temperature is above 425 degrees Fahrenheit (218.333 degrees Celsius). [7] Also, the tin coating wears away with time. In order to protect the coating, one should use wooden or silicone spatulas and avoid cooking acidic foods.
Kalai can be done in various ways. Virgin grade tin (called ‘ranga’ in Hindi), caustic soda, sal ammoniac (ammonium chloride, called ‘nausadar’ powder in Hindi), and water are used in the process. [6]
The first step of kalai is to clean the utensil with water. There are two ways of cleaning the utensil further to remove any impurities such as dust. The first is to clean it with caustic soda. The other is to wash it with dilute acid solution which contains a gold purifying compound known as ‘sufa’. If the latter is used, the utensil should be cleaned immediately after applying the dilute acidic solution as it may bear a mark if not done immediately.
After the cleaning, the vessel is heated on burning coal for about 2 to 3 minutes. The Kalaiwala, Kalaigar or Kalaikar then digs a small pit in the ground to burn the coal. He/she prepares a temporary blast furnace to do kalai and blows air through bellows. After the vessel turns pinkish hot, virgin grade tin (in the form of strips) is applied on the hot vessel. This step is called ‘casting’ by the Kalaigars. The ‘nausadar’ powder is sprinkled on the vessel. The tin melts rapidly which is then rubbed evenly on the utensil with the help of a cotton cloth or a swab of cotton. The rubbing process is known as ‘majaay’ in Hindi. A whitish smoke with the peculiar smell of ammonia is released when the ‘nausadar’ powder is rubbed on the utensil. A silvery lining appears on the vessel with a shine. The final step of kalai is to dip the utensil in cold water. [3] [8] [9]
Kalai was earlier done with silver instead of tin but now it would be too expensive. [10] As stainless steel and aluminum ware came into being, the usage of copper and brass utensils decreased, which led the Kalaigars to suffer losses. [3] Nowadays only some hotels and a very few people use vessels with kalai. [11] As a result, there are a very few Kalaigars left and the art of kalai is vanishing.[ citation needed ]
Electroplating, also known as electrochemical deposition or electrodeposition, is a process for producing a metal coating on a solid substrate through the reduction of cations of that metal by means of a direct electric current. The part to be coated acts as the cathode of an electrolytic cell; the electrolyte is a solution of a salt whose cation is the metal to be coated, and the anode is usually either a block of that metal, or of some inert conductive material. The current is provided by an external power supply.
Cookware and bakeware is food preparation equipment, such as cooking pots, pans, baking sheets etc. used in kitchens. Cookware is used on a stove or range cooktop, while bakeware is used in an oven. Some utensils are considered both cookware and bakeware.
Sodium silicate is a generic name for chemical compounds with the formula Na
2xSi
yO
2y+x or (Na
2O)
x·(SiO
2)
y, such as sodium metasilicate, sodium orthosilicate, and sodium pyrosilicate. The anions are often polymeric. These compounds are generally colorless transparent solids or white powders, and soluble in water in various amounts.
Trisodium phosphate (TSP) is an inorganic compound with the chemical formula Na3PO4. It is a white, granular or crystalline solid, highly soluble in water, producing an alkaline solution. TSP is used as a cleaning agent, builder, lubricant, food additive, stain remover, and degreaser.
Rosin, also known as colophony or Greek pitch, is a solid form of resin obtained from pine trees and other plants, mostly conifers, primarily through heating fresh liquid resin to vaporize the volatile liquid terpene components. Used widely in various industries and arts, rosin appears as a semi-transparent, brittle substance that ranges in color from yellow to black and melts at stove-top temperatures. Rosin consists mainly of resin acids, especially abietic acid, and is soluble in alcohol, ether, benzene and chloroform.
Gilding is a decorative technique for applying a very thin coating of gold over solid surfaces such as metal, wood, porcelain, or stone. A gilded object is also described as "gilt". Where metal is gilded, the metal below was traditionally silver in the West, to make silver-gilt objects, but gilt-bronze is commonly used in China, and also called ormolu if it is Western. Methods of gilding include hand application and gluing, typically of gold leaf, chemical gilding, and electroplating, the last also called gold plating. Parcel-gilt objects are only gilded over part of their surfaces. This may mean that all of the inside, and none of the outside, of a chalice or similar vessel is gilded, or that patterns or images are made up by using a combination of gilt and ungilted areas.
Patina is a thin layer that variously forms on the surface of copper, brass, bronze, and similar metals and metal alloys, or certain stones and wooden furniture, or any similar acquired change of a surface through age and exposure.
Tarnish is a thin layer of corrosion that forms over copper, brass, aluminum, magnesium, neodymium and other similar metals as their outermost layer undergoes a chemical reaction. Tarnish does not always result from the sole effects of oxygen in the air. For example, silver needs hydrogen sulfide to tarnish, although it may tarnish with oxygen over time. It often appears as a dull, gray or black film or coating over metal. Tarnish is a surface phenomenon that is self-limiting, unlike rust. Only the top few layers of the metal react. The layer of tarnish seals and protects the underlying layers from reacting.
Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts.
Purified water is water that has been mechanically filtered or processed to remove impurities and make it suitable for use. Distilled water was, formerly, the most common form of purified water, but, in recent years, water is more frequently purified by other processes including capacitive deionization, reverse osmosis, carbon filtering, microfiltration, ultrafiltration, ultraviolet oxidation, or electrodeionization. Combinations of a number of these processes have come into use to produce ultrapure water of such high purity that its trace contaminants are measured in parts per billion (ppb) or parts per trillion (ppt).
Copper electroplating is the process of electroplating a layer of copper onto the surface of a metal object. Copper is used both as a standalone coating and as an undercoat onto which other metals are subsequently plated. The copper layer can be decorative, provide corrosion resistance, increase electrical and thermal conductivity, or improve the adhesion of additional deposits to the substrate.
Tinning is the process of thinly coating sheets of wrought iron or steel with tin, and the resulting product is known as tinplate. The term is also widely used for the different process of coating a metal with solder before soldering.
Clean-in-place (CIP) is an automated method of cleaning the interior surfaces of pipes, vessels, equipment, filters and associated fittings, without major disassembly. CIP is commonly used for equipment such as piping, tanks, and fillers. CIP employs turbulent flow through piping, and/or spray balls for tanks or vessels. In some cases, CIP can also be accomplished with fill, soak and agitate.
Black oxide or blackening is a conversion coating for ferrous materials, stainless steel, copper and copper based alloys, zinc, powdered metals, and silver solder. It is used to add mild corrosion resistance, for appearance, and to minimize light reflection. To achieve maximal corrosion resistance the black oxide must be impregnated with oil or wax. Dual target magnetron sputtering (DMS) is used for preparing black oxide coatings. One of its advantages over other coatings is its minimal buildup.
A kitchen utensil is a small hand-held tool used for food preparation. Common kitchen tasks include cutting food items to size, heating food on an open fire or on a stove, baking, grinding, mixing, blending, and measuring; different utensils are made for each task. A general purpose utensil such as a chef's knife may be used for a variety of foods; other kitchen utensils are highly specialized and may be used only in connection with preparation of a particular type of food, such as an egg separator or an apple corer. Some specialized utensils are used when an operation is to be repeated many times, or when the cook has limited dexterity or mobility. The number of utensils in a household kitchen varies with time and the style of cooking.
Bronze disease is an irreversible and nearly inexorable corrosion process that occurs when chlorides come into contact with bronze or other copper-bearing alloys. It can occur as both a dark green coating, or as a much lighter whitish fuzzy or furry green coating. It is not a bacterial infection, but the result of a chemical reaction with the chlorides that usually occurs due to contamination of the bronze object by saltwater or from burial in specific types of soil where chloride salts are present. If not treated, complete destruction of the affected artifact is possible. Treatment is very difficult, costly and not always effective. Transfer of chlorides from the contaminated artefact to other artefacts can spread the condition.
Bismuth bronze or bismuth brass is a copper alloy which typically contains 1-3% bismuth by weight, although some alloys contain over 6% Bi. This bronze alloy is very corrosion-resistant, a property which makes it suitable for use in environments such as the ocean. Bismuth bronzes and brasses are more malleable, thermally conductive, and polish better than regular brasses. The most common industrial application of these metals is as bearings, however the material has been in use since the late nineteenth century as kitchenware and mirrors. Bismuth bronze was also found in ceremonial Inca knives at Machu Picchu. Recently, pressure for the substitution of hazardous metals has increased and with it bismuth bronze is being marketed as a green alternative to leaded bronze bearings and bushings.
Rewari metalwork refers to the metallurgy practised by the native people of the city of Rewari, India. The items produced are commonly made of brass, and are often possessed with cultural and utilitarian value. The practice is known to have been in place as early as the 16th century.
Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte. A similar galvanic reaction is exploited in primary cells to generate a useful electrical voltage to power portable devices. This phenomenon is named after Italian physician Luigi Galvani (1737–1798).