Glazed Stone Proof

Glazed Stone Analysis Proves Furnaces
At Spruce Hill Were Metallurgical

Celedon glazes on Spruce Hill furnace debris are proof that temperatures around 2300 degrees F were reached; implying the use of both a powerful air blast and charcoal fuel. The glaze results from the reduction of red clay mortar, which contains iron oxide. Red clay is commonly used as a refractory mortar in furnaces, but would liquefy if the high temperatures and reducing conditions of a furnace were significantly increased by a sudden blast of high speed wind. Such sudden blasts of wind often occur on the westward facing hilltop where this fragment was found.

This piece of sandstone furnace debris was collected from the western wall of the Spruce Hill Works by the author of this web site near "Point F" of the Squier and Davis Map. This page analyzes the artifact for its ceramic properties.

An upward pointing droplet indicates that the large surface shown was facing down in the furnace wall. Most of the flat surface is covered with clear Celedon glaze. Celedon remains clear when covering a light surface, but darkens when covering a darker one. Thus the dark glaze covers a red surface of the sandstone (Dark Edge above).

Other edges labeled "red" or "tan" are not covered with glaze. Areas marked "M" show where remnants of the red clay mortar were not reduced to glaze. The red edges are evidence of exposure to indirect heat from the furnace, and possibly these portions of the stone were imbedded in the furnace wall. The tan edges are probably places where the stone was broken when the walls containing the furnaces were destroyed. Tests of Spruce Hill sandstone show that at prolonged exposure to temperatures around 2300 degrees F the stone loses tan or red color and is bleached white. Thus the red area beneath the glaze was covered before it could be bleached white.

Historical, Geological Analysis

How Walls and Furnaces Were Destroyed

No intact furnace may remain at Spruce Hill. Destruction of the walls and furnaces long before and following Foster's 1811 visit apparently were the result of several causes:

Visitors to Spruce Hill in the early 1800s said the walls were overgrown with very large trees and littered with large tree trunks and branches. So before 1800, the walls must have been disturbed by many cycles of tree growth. When old trees are uprooted at the edge of the windy hilltop they pull up large root balls. This would pull apart walls and furnaces.
Spruce Hill dominates the skyline south of the Ross County village of Bourneville. According to residents of the village and surrounding area, the hill was something of a playground for local residents during the 19th century. Also, the stone walls were used as handy source for all sorts of local uses of stone, and sometimes stone was hauled away by the wagonload.
Amateur archaeologist Arlington Mallery once used a bulldozer to uncover what he reported as remains of an ancient iron smelting furnace at Spruce Hill. Also, according to local residents, the landowner once leveled some of the walls with a bulldozer after becoming irate about trespassing by curious folks after newspaper stories about Mallery's investigation there appeared.
George Shoemaker of Bourneville apparently set off a minor "gold rush" at Spruce Hill in 1919 when he found "fool's gold" in what Mallery later claimed was a large pit iron furnace. Shoemaker emptied this stone lined pit, 12 feet long, 9 feet wide and 2 feet deep of its contents of cinders, rotted wood, bits of charcoal and glazed pieces of sandstone. This pit, which was shown to me by Mallery in 1963, seems in retrospect not likely the remains of an iron smelter.

A Natural Wall-Wrecking Machine

Large trees along the western wall of Spruce Hill are rooted in loose red Berea sandstone and soil. Craig Huhman holds a piece of this red sandstone which was used in constructing the laid-up wall of loose stones in prehistoric times.

The destructive potential of the toppling of trees on the walls and any furnaces in the walls is evident in this photo, taken during an APG Society expedition May 28, 1995.

Bret J. Ruby, then archaeologist of the Hopewell Culture Historical Park, US Park Service, was a member of the tour, conducted by David Orr and this writer. Photos by author.

'Paint Ore' Deposit At Plateau's Edge

Craig Huhman, left and Don Thomas, right, examine a handful of red "paint ore" from this deposit on the edge of the Spruce Hill plateau. Apparently this heavy red clay provided the refractory mortar for joining the sandstone pieces of the metallurgical furnaces.

Small deposits occur as "mini-bogs" at random along the hilltop's edge, suggesting that basins created by tree uprooting allow pockets of paint ore to be naturally formed from weathering of the red sandstone. According to Pough, the hematite form of iron ore can occur as soft, red earthy masses of "paint ore."

References

Daniel Rhodes, Clay and Glazes for the Potter, rev. ed. Chilton, Radnor, PA, 1973.

Pough, Frederick H., Rocks and Minerals, Hough Mifflin Co., Boston, 1976.

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