This post examines the chemistry of vitrification
to determine if there is a link between the vitrified stones that are found in Iron Age Scottish hillforts and in the ancient megalithic
stone work of South America.
The vitrified stones in the walls of the hillforts
in Scotland appear haphazard and look like
they were the result of accidental or intentional
fires rather than the deliberate application
of heat technology. The stones are fused with
evidence that gas bubbles formed within the
melted rock, and the vitrified walls have
a coarse appearance that is not aesthetically
Theories Of Melting The Rocks To Combine These Structures
There is no lime or cement in these structures, all of them are reinforced to some extent by the fusion of the built rocks. In extreme heat conditions, this merger was not as complete in another fortress or even on the same fortress wall. In some cases, the stone is partially melted and calcinated. Otherwise, the adjacent edges are joined and glued tightly. In most cases, the pieces of stone are wrapped in a coating such as glass enamel and held together.
Though it is not clear why or how the walls were subjected to vitrification. Some historians have argued that it was done to strengthen the wall, but in contrast the heating actually weakens the structure.
By contrast, the vitrification of the megaliths
in South America seem to have been made using
well-established technology. Weathering has
crumbled away parts of the vitrified crust
in some stones, revealing a rougher surface
underneath. Many stones have retained their
sheen for hundreds or perhaps thousands of
A high temperature is required to melt stone.
Lava from volcanoes is produced at temperatures
of about 1200 degrees Celsius. After cooling,
lava can vitrify to form glasslike substances,
such as black obsidian. Ordinary wood fires
usually are not hot enough to melt stones.
A study of the Dun Deardail hillfort in Scotland
found that the tops of the stone walls were
the most heavily vitrified. This can be explained
if ashes of a burning superstructure on top
of the wall fell on the rocks during a fire.
This will become clear when we take a look
at Iron Age fort construction and vitrification
with wood ashes.
The Iron Age fort of Biskupin in Poland was
occupied from about 800 to 475 BC. Its reconstruction
helps to visualize the typical features of
Iron Age forts. The ramparts or defensive
walls of Iron Age forts were thick to be able
to hold wooden watch towers with thatched
roofs to protect the guards from the rain
and cold. The thick walls allowed defenders
to climb on top and fight the enemy with slings,
arrows and other projectiles. The Scottish
forts were constructed with wooden beams and
drystone instead of the packed dirt of the
For defense, the forts were surrounded by
moats and fortified with stockade fences.
When the wooden structures and thatched roofs
on top of the ramparts caught fire, the hot
ashes dropped on the stones of the wall and
acted as a flux that lowered the melting point
of the rock wall to cause vitrification.
Ash glazes are ceramic glazes made of the
ash of wood or straw. A wood fire can provide
the chemical components for vitrification,
particularly when burning timbers and a thatch
roof fall on top of the stone ramparts. Wood
ash contains 25 to 45 percent of calcium carbonate,
about 10 percent of potash, and less than
one percent phosphate and other trace elements.
Potash is mainly potassium carbonate. Ash
glazing began initially by accident around
1500 BC in China during theÂ Shang Dynasty
as ash from the burnt wood in the kiln landed
on pots. Around 1000 BC, the Chinese started
adding the ash before the pot went into theÂ kiln.
Ash glaze was the first glaze used in East
Asia, and contained only ash, clay, and water.
In Korea, a traditional ash glaze is still
used today for Onggi pots used for cooking
and for fermenting foods such as kimchi. The
glaze consists of finely ground wood ash and
leaf mold made into a thin slurry that is
applied to the pots by dipping. After the
pots are fired in a kiln they come out with
a lustrous vitrified sheen from the wood ash
glaze. This traditional glazing technology
provides the basis for the hypothesis that
the vitrification of the Scottish forthills
was caused by accumulation of wood ashes on
top of the stone walls when the fort was on
One Possible Explanation of Vitrification Of Megaliths in South America
We now take a look at the vitrified megaliths of South America. Graham Hancock's web site has an article by Jan Peter de Jong and Christopher Jordan that describes the vitrified stonework in the Inca vestiges of Peru. The article mentions that a small stone sample from the Peruvian site called Tetecaca was tested and
that the main body of the stone shows the spectral composition of limestone with high levels of calcium, carbon, oxygen and minor trace elements.
This is expected since the
Sacsayahuaman archaeological park is on a karst landscape of limestone bedrock.
The vitrified surface of the stone shows a very different spectrum of elements compared to the limestone body. The main difference is that silicon is the predominant component and oxygen, aluminum and magnesium are also significantly higher than the body of the stone. Calcium and carbon are much lower thanthe body sample. The silicon, aluminum and magnesium seem to indicate that a material was added to the surface of the stone.
We should keep in mind that oxygen, silicon and
aluminum are the three most common elements
of the Earth's crust and that they are the constituents of clay minerals which are hydrous
aluminum phyllosilicates with molecular formulas
containing 3 atoms of silicon or aluminum for every 4 atoms of oxygen.
The chemical decomposition of limestone with heat and the reaction of the resultant compounds with water and carbon dioxide in the air can shed some light on the process of vitrification.
Limestone is basically calcium carbonate, which decomposes at a temperature of 825 degrees
Celsius into calcium oxide and carbon dioxide.
Calcium oxide is commonly called quicklime,and it reacts with water to form calcium hydroxide and heat. Calcium hydroxide, also called slaked lime, is a component of bricklayer's mortar and it turns back into limestone by reacting with carbon dioxide in the air. From these reactions, it is clear that a cycle of heating and cooling limestone can change the characteristics of the surface.
Let us say that a slab of limestone is heated so that quicklime forms on its surface. Afte the slab cools down, the surface may be covered with a layer of moist clay that will integrate the aluminosilicates of the clay with the quicklime in a thin layer that hardens into a type of Portland cement, which is basically
a mixture of quicklime, silica and alumina.
Variations of this procedure may have been
used for vitrification of some South American limestone surfaces.