Post 706 -by Gautam Shah

Part -II will deal with ADDITIVES for CLAYS



Surface finishes and Products composed with CLAY as the prime raw material have been used, for every conceivable purpose and in all parts of the world. Clay is preferred for : Abundant supply, cheapness, universal availability, insulation qualities, ecological value and simplicity of application. Clay finishes and products have some drawbacks like: shrinkage on drying, i.e., cracking, poor weathering qualities, lack of homogeneity in dry state, high water permeability -hygroscopic, poor bonding to a substrate peel-off, vulnerability to white ants and insects.


The quality of the clay-based surface finishes and products depend on:

  1. Quality of soil
  2. Fillers
  3. Additives
  4. Manufacturing processes


Quality of Soil

Soil is a product, formed mainly from the decomposition of a rock and ashes of lava origin. The decomposed product may remain at its place of origin or get transported to other places by natural forces like water, wind etc. The product, which remains at the place of origin the Residual clays, are comparatively pure, but have less uniform particle size distribution. Materials that after being transported get deposited somewhere else are the Sedimentary or secondary clays. These are generally contaminated by other materials and have smaller but uniform particle size distribution.

Red Iron rich Earth

Principal constituents of clays are Alumina and Silica. Alumina provides the plasticity, and Silica, if free, reduces the shrinkage and warping. Composite silica, though increases the warping on baking. Other elements of clays are Calcium, Magnesium, Iron, Manganese, Potassium and Sodium. Various compositions of these elements and their crystalline structure affect the quality, colour and texture of the soil. Kaolin is the chief constituent of clays used for Ceramics production.


Clays used for products making and surface finishing, are either Top-organic soils or Virgin-non organic soils.


Top-organic soils have substantial amounts of organic matters from the decomposition of vegetation and human, and animals excrete. The presence of organic matters makes a soil light in weight and dark in colour. Organic soils usually show high workability and low shrinkage characteristics. When organic soils are found below an existing layer and are old, contain gallic acid and tannin in small proportions but sufficient to act as fungicide and mild insecticide.


Virgin or non organic soils have negligible amounts of organic matters, and so reflect the basic characteristic of the predominant constituent element, i.e., lime, silica, or alumina. Non-organic soils, however, do take-on the personality of the other minor minerals present in it. Iron oxide as ferric and ferrous is the most important colourant. Other important colourants are quartz, kaolin, mica etc. Soils show a wide range of colours from off-white to yellow, light brown and chocolate to reddish tones. Non-organic soils unless constituted by colloidal particles show very little plasticity. Some mineral constituents of such soils are reactive to water resulting in swelling and leaching.


Residual or sedimentary materials available at the top of the surface, or below a certain depth, can be classified as: Clays, Sands, Silt, Shale, Colloids, Hard pan, Hoggin, Loam, Peat-Muc, Humus.


Clays are fine albuminous products formed by decomposition of igneous rocks (lava activity). Clays are tenacious and plastic when wet. Clays are highly cohesive, have high capillaries and no internal friction. Clays are smooth to touch, sticky and plastic. Clays can also be classified according to their plasticity, or silt content. Hard clays or stiff clays have low sand content, and are difficult to excavate. Fine clays have medium sand content, and can be excavated with slight effort. Soft clays have coarse texture and are easy to excavate. Pure clays are mostly useless because of the high plasticity and excessive shrinkage on drying. Plastic clays are called fat clays, and less plastic clays and are also called lean clays.

Ball ClaysClays are black, white, red, brown and yellow in colour. China Clay is a residual material, contaminated with silica, mica, feldspar and decomposed feldspar. Ball clay is a sedimentary material of fine grain size and some organic contents. It is finer than china clay. Fire clays are formed from feldspar as residual and sedimentary deposit. Brick clays are high in iron content, and impurities of calcium compounds and organic matter.


Sands are of small granular particles, usually of stones. Sands are gritty to touch, with little cohesion. It has high internal friction and very little capillarity. Silts are soils that are somewhere between a clay and sand. Silts are slightly gritty to touch and are darker in colour than clays. Colloids are gluey matter found with clays but of ultra fine particles. The colloids absorb moisture and remain suspended, rather than settle down in water. Shale is a compressed and laminated clay with or without organic matter. Shale is plastic when wet but disintegrates when dry.

Volcanic ash deposition

Hard pan is a very dense accumulated mass of soil, consisting of clay, sand, gravel, etc. held together in a rock like but layered formation. Hard pan does not soften when wetting. Hoggin is a natural deposit of a mixture of clay with small stones, grit and sand. Loam is a soft mixed deposit of silty clay and sand in different proportions. Peat-muc and Humus, have fibrous or spongy organic matters formed by the decay of plants. These deposits are black or dark brown in colour, varying compressible in presence-absence of water and so unsuitable for heavy loads. The decomposition of organic material is more advanced in muc than in peat.




Post 334 – by Gautam Shah


We seek material objects with perfect combination of Engineering attributes, Dimensional features and Surface properties. Our quest is further complicated when we require materials in very large quantity and consistent quality. We often need the materials locally and immediately. The quest for the materials proceeds along these courses.

Strategy –ONE

We usually have some idea how a particular material will function in a given situation. And so we SELECT the most appropriate material for its probable response. We primarily pick such materials off the surface of earth or mine it. But it would be very rare for anyone to find a Natural Material with perfect combination of all the essential qualities.

Natural pick up for a purpose

Adobe Building

Strategy –TWO

Natural materials have certain inherent efficiencies. We retain these, yet widen our options by dressing, cutting, and carrying out other modification processes. The size of a Modified Natural Material, remains the same or in most cases gets decreased. It is also not possible to achieve a material with distinctly different qualities, then what the nature offers.

Stone Implement

Kengo Kuma -Commune by the Great Wall of China

Strategy –THREE

Natural, modified (and often manufactured materials) have limitations of size, and variations of colour, texture, patterns, etc. One needs to assemble a larger entity. Agglomerated Materials are composed by closely placing the units with or without an alliance (exchange of ions), or by joining or adhering with an agent. The agglomerated materials also have a new variant, -the joint. The agglomerated entity remains as weak as its weakest constituent, usually the joint.

Log Cabin an assembly of natural material but joint always weak

Cain Natural material geometric assembly

Strategy –FOUR

Quality of natural, modified or agglomerated materials can be tempered with certain treatments and processes. The treatments are like annealing, hardening, seasoning, wetting, etching, ph balancing etc. Processed materials can have treatments that are surface bound or affect the whole body of the material.

Tempering a material

Strategy –FIVE

In spite of all the modifications, aggregation and processing the dimensional limitations of materials remain. An assured quality can only be achieved by producing a new material out of a raw material. Manufactured Materials are produced from raw materials that apparently have little or direct use. Manufacturing involves several levels of processing, before the resultant product can have some utility. Manufactured materials have completely different quality in comparison to their ingredients. Manufactured materials have some dimensional limitations, as imposed by the methods of manufacturing (batch size, machine capacity -eg. textiles, rexine, plywoods). Though, coatings and other deposition techniques overcome the size restraints.

Extruded Aluminum sections

Strategy –SIX

A manufactured-material is further processed to create Components, or several materials are mixed to form Compounded Material-Product. Natural and manufactured materials are also combined to create Composites (e.g. composites, co-extrusion), or chemically blended (co-polymerization) to form Synthetics. Components, compounded material-products, composites and synthetics, all are further exploited geometrically, to form Systems. Such systems have dual, Functional and Structural identities.


Silicon carbide (SiC), also known as carborundum

The term Synthesis refers to how materials are made from naturally occurring or man-made chemicals. The term Processing means how materials are shaped into useful components to cause changes in the properties of different materials. –The science and Engineering of Materials : Askeland & Phule.

We primarily endeavour to create Single Material Objects. Single material-objects, be it natural or man-made have inherent efficiencies. We try to achieve the state of a single material efficiency by integrating (composites) or by synthesizing materials (synthetics). Such materials are commercially called multi purpose materials.

A Multi purpose material to be effective requires redefining of the geometry (form of construction) of the entity. Such redesign takes years of research effort. Human ingenuity, however, can outpace such attempts by inventing superior, but totally a different entity, for the given situation. The superiority of a newly invented entity may happen, because of its unitary structure, or as a multiplex system of simpler and lesser number of elements.




Post 257 – by Gautam Shah 


Main Objectives of Materials Processing:

  1. Shape and size formation
  2. Alteration and induction of properties
  3. Endowing finishes



Body forming processes change the dimensional format of the material through phase-change of the material (solid to liquid to gas, or vice versa), within the same material phase (heat treatments, hot and cold working, and through mechanical work like mixing, stirring), and through material compositions (structuring, assembly).


Grains or dust mixed with a binder material can be cast into solids, or melted-fused as alloy, or sintered to a ceramic. Solids can be rolled into sheets or melt-spun into fibres, ground to powders, or drawn into wires. Fibres and wires are woven into fabric sheets.

Shop Copper Tableware Old Antiques


  • Solid forming: Forging, beating, pressing, rolling, drawing, casting, extrusion, moulding.
  • Sheet forming: Bending, punching, stamping, cutting, seaming, forming, moulding.
  • Linear forming: Drawing, spinning, entwining, weaving.
  • Grain forming: Blowing or granulation, chopping, grinding.


Expanded Metal lattice

Shaping processes can also be classed as:

1a  Flow processes: casting, moulding, extruding, drawing, rolling, forging, hammering, beating, powder-technology, material deposition, stamping, punching, pressing, bending, folding, seaming.


1b  Additive processes: lamination, crystal growth, foaming (lower phase material dispersion in a higher phase material), plating, cladding, mounting, joining, material deposition, fabrication, joining, supporting, holding, keying, positioning, plugging, arranging.


1c  Reducing processes: cutting, chopping, sizing, splicing, scooping, drilling, boring, machining, planning, chiselling, chipping, grinding, rubbing, sand blasting, cleaning, washing, melting, dissolving.

1d  Other forming processes: spinning, weaving, knitting.



Alteration and Induction of properties cause a change in the engineering or structural quality of the material, frequently accompanied by the modification of the surface characteristics. The alteration processes are also designed to regain the lost or the reduced properties during other processing.


2a  Heat treatments: boiling, liquidizing, melting, softening, sintering, baking, drying, fusing, welding, soldering, forging, annealing, heating, hardening, crystal forming, blowing.

2b Non heat treatments: magnetizing, static discharging, infection proofing, cleaning, washing, earthing, wetting, drying, stretching, strenting, stressing, compressing, stretching (tensile), twisting, filling.

2c  Material applications: coatings, depositions, claddings, Panellings, enamelling, inlaying, gilding, printing, moisture proofing, fuming.

2d  Non material processes: embossing, engraving, polishing, burring, charring, burnishing, chasing, buffing.

2e  Chemical treatments: dyeing, bleaching, etching.

Artist Pottery Decoration Ceramic Blue Pot



Finishes are created: By altering the surface properties of the materials at a raw material stage and also after the formation of the object, By reforming the objects, and By applying other materials at a raw material stage or at an object formation stage.

The need for a peculiar finish could be varied, but essentially for: Imparting specific sensorial characteristics, for survival of the object in an environment, for changing the structural properties, as an aid in material processing and forming operations, for storage and handling of the raw materials or components, and for receiving the next treatment.

3a  Processes for Natural Surface Finishes: Natural Finishes result due to many different factors, such as: Elemental conditions of formation, subsequent responses like weathering, cognitive affectations, and later, natural or man-made interventions (angle of cut, tools and techniques used, etc.).


Natural surface finishes have three main cognitive affectations: Colour, Pattern and Texture. The colours are of original formation, subsequent weathering, readjustment of stresses, or induced by physical and chemical changes. The patterns result from the stresses, mixing of constituents, weathering, and the varied reactivity of different parts and constituents. Patterns also result from granular or fibrous orientation, method of cut, cyclic nature of growth, formation of residual products, deposition of contaminants, and tools-techniques of handling and processing. Textures primarily result from the degree of homogeneity, angle of cut, differential weathering, and various formative processes.


3b  Processes for Manufactured Surface Finishes: Manufactured Surface Finishes result at three levels: Raw material stage, Product formation stage, and later, through Application of surface finish on completion of the system. In an integrated production setup all three could be a single stage or plant process, but in most other fabrication shops only the last two processes are combined. For a site fabricated systems like buildings, the last process, i.e. surface finish application, is a distinct process as it is carried out at a site. Manufactured surface finishes as a result are of two categories: Plant based and Site-based systems. Though lot of preparatory work may occur in the industrial plant for the site-based surface finish application. Products fully surface finished in industrial plants require very careful handling (transportation, loading, storage, delivery and positioning), and so may carry protective but removable coatings or shields.