Saturday, September 7, 2013

PRIMITIVE COATINGS Surfaces, Materials and Techniques

PRIMITIVE COATINGS    Surfaces, Materials and Techniques     article - II in series Coatings

Coatings have been used for coating and decorating many objects and surfaces for the past 60000 years. ‘Coatings’ were used to add colour, add a protective layer, ‘plaster’ a surface, impart a pattern or an identity signage. The coatings materials were mostly of natural origin such as available off the ground, or from animals and plants. The act of coating was intentional, done with a sure purpose. But it had a wondrous effect that gave a new purpose to the artefact. Coatings’ techniques used for painting became a magic media to express what spoken language could not do.

Objects and surfaces to be coated:

A primitive person, for the supposedly unencumbered life, had many objects that could receive coatings. These objects had natural or formed shapes and surfaces. The surfaces had different porosities, textures, base-colours and patterns (grains, patches, stains, etc.). The objects were hides, skins, bones, teeth, stones-rocks, ‘precious stones’, sea shells, dry leaves, plant fibers, wood, raw and baked clay products, and of course own body parts such as hair, skin, nails, teeth, etc. Some of the surfaces such as the hides were cleaned and shaved by heavy rubbing. Bones were ground to remove the sheen and make surface slightly rough and absorbent. Stones and woods were polished or scrapped. Raw and baked clay products were re-fired after coating. Leaves were rolled, pressed and dehydrated at the green stage by burying in layers of ash or sand.
Coating Materials:

Coating materials of the primitive age are still being used in many situations and so continue to be relevant. Blood is perhaps the earliest colourant. It is a liquid of rich colour, representing the vibrancy of life and the metaphorical power over the kill. However, blood has very weak colour integrity and it is biologically highly degradable material. Wood coal is a dry colourant, easy to handle. It requires a textured base for ‘rubbing-in’ or a binding liquid to form an applicable paste. Carbon (Lamp) Black -a deposition collected over burning fat or oil, is much better due to oil content. Whites were procured from metallic oxides and carbonates. Lime is most common everywhere. Iron Oxides are equally common, and have many different hues (such as yellow, brown, red and black). Oxides are very stable and ‘deep’ (high saturation) colours.

In this palette the notable absence was of Green and Blue colours. Brilliant Red that could represent the fresh blood, and Pink of the meat were also absent. Absentee colours were sought from plants, flowers and fruits. These were Yellows, Orange, Greens, Mauve and Purple. However, plants, seed and fruit juices were of low opacity (transparent), sun light fading and biodegradable colours.

Binding materials and techniques:

The colour palette was of mostly of dry powders or soft rocks. These had poor binding to the substrate. Liquid juices were absorbed into the surface. By heavy rubbing the colour pigments got trapped in the micro cavities of the surface. Some form of binding material or technology was needed. Water was used as a carrier agent, but its binding was only temporary. Plant oils, mutton fats, fish oils, etc. were used to fix colours. However these oily substances were ‘non-drying’ and remained wet for a long time. The wet surface attracted dust and trapped insects. The oily substances deteriorated and on oxidation turned dark in colour.

Proteins-based materials like blood, eggs, milk, urine, starches were also used as binding materials. Plant and insect exudates or natural gums had binding properties but were highly hygroscopic (affinity with water) materials. Plant milks or latexes, like materials, were also used. Wax was used to mix with pigments and as a protective layer. Wax and Natural Creosote were used to protect wood and leather surfaces.

Slaked lime and pozzolana (volcanic) ash, were two alkaline materials that had binding properties. However, lime when mixed with a colourant imparted a white shade creating a ‘pale’ effect. Pozzolana had darker colour so made the colourant several shades darker. Clays of various mineral contents were also used to bind the pigments. Plastering and daubing were frequently used to prepare a better surface for a wall painting.

Some mechanical processes were used to help coating application. These were surface rubbing, hammering, scrapping and shaving (for leather surfaces), heat burnishing and surface sintering.
Primitive binding materials can be categorized in several ways:
  • Natural binding properties versus the water wettable/ reducible materials, 
  • Drying versus non drying,
  • Water wettable or hygroscopic versus water resistant materials.

With vast array of surfaces to be coated and availability of wide variety of colourants led to experimentation. By the time of stone age refining and upgrading of colourants was achieved. Surface finishing techniques were much refined.

Three outstanding technologies were devised.

1  It was application of plaster with and without colourants,
2  It was pigment refining, sintering and grinding,
3  It was colouring ceramics before firing to create a permanent colours.

  • The earliest known cave paintings date from about 32,000 BC. Lascaux, an underground cave (15000 to 9000 B.C.), located in south-western France, has walls and ceilings, decorated with some 1,500 engravings and about 600 paintings in shades of yellow, red, brown, and black. The sheer scale of the paintings suggests that ladders and scaffolding must have been used. Charcoal, lamps, spear points, pigments, and engraving tools were discovered on the floor of the cave. When the cave was discovered, the paintings were in a very fine state of preservation, due to the stable levels of moisture and temperature within the cave, providing an ideal environment for the preservation of pigments over thousands of years. However soon after being opened to the public, the paintings began to deteriorate, colours beginning to fade, and a green fungus  grew over the pigments.

  • The pigments of cave paintings probably have been preserved by a natural  process of rainwater seeping through the limestone rocks to produce saturated bicarbonate. The colours were rubbed across rock walls and ceilings with sharpened solid lumps of the natural earths. Outlines were drawn with black sticks of wood charcoal. The discovery of mixing dishes suggests that liquid pigment mixed with fat was also used and smeared with the hand. The subtle tonal gradations of colour on animals painted in the Altamira and Lascaux caves appear to have been dabbed in two stages with fur pads, natural variations on the rock surface were exploited to create the effects of volume. Feathers and frayed twigs may have been used in painting manes and tails.

The Coating Application Processes:

The simplest way of marking cave walls was to make finger-nail traces in the soft layer of clay covering the rock. Lime stone walls were engraved and filled in with iron oxide (hematite, or ochre), or the black pigment such as the manganese or charcoal. These materials were usually available locally. Analyses of pigments, reveal the use of extenders (dull or low opacity powders) such as talc or feldspar, to increase the bulk of pigments. The coating also shows traces of animal and plant oils, used for either for binding or as a protective covering. The pigment in paste form was applied with fingers, and also tools like fiber pads, animal-hair brushes or crushed twigs. Lumps of pigments discovered on the floor of caves were perhaps used as crayons, or were grinding onto colour powder. Colours were often sprayed, directly from the mouth or through a tube. A network of ladder, supports and scaffolding was used to reach the ceilings and upper portions of walls. Light was  provided by hearths, or portable burning torches. The coated surfaces were ground to achieve a sheen on the surface or re-coated with protective layer of egg-whites, oils or fats.

The primitive age craft of coating can be summed up as Surface preparation, Application of the coating, Applying tonal variations or shades, and Covering the surface with water protective coat, usually of oils or other transparent materials.

Next Blog post in continuation of this series
Coatings in Iron age

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