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The Slag Page

A blast furnace produces two products: one is the pig iron that is the marketable/usable product and the other is slag that is typically discarded at the site. It was used later for roadkill and also apparently used to make some variants of Depression Glass. It is proof positive that the furnace actually went into blast (production). At Falling Creek, not one piece of glassy slag has yet been recovered. Just one piece would confirm that they got into production before the March 22, 1622 attack by the Powhatans. Please keep an eye peeled when walking around on the site as you may find the first piece.

Noble Furnace in Wythe County was in operation over 4 years and yet there is nearly no visible slag on the ground. The amount of slag from the Falling Creek venture would be quite limited due to the short period of time they were in blast. From the surviving letters, it is possible they got into blast late in the 1622 season, but unlikely. The letters indicate they were still in construction. But they would have started as soon as the threat of freezing the water wheel disappeared which could have been as early as late January of 1622. This is why finding just one piece of glassy slag is so vitally important.


Furnace Slag

Blast furnace glass is solid, shiny and as it is glass, it is sharp and it will cut. Any transfer to your hand will not be from the slag itself, but from the dirt surrounding it that may be nestling into the bubble holes.

The purpose of these Slag pages is to show some examples of each from various furnaces.



Noble Furnace
Noble Furnace & Casting Shed

Blast furnace slag is distinctive. It is a dense glass. The colors come both from minerals and elements within the iron ore and the fluxing agent. There is archaeo-metallurgical discussion going on as to whether the process or the ingredients or both and if so, how much of either, if any, influenced the color. Two sides have apparently equally valid arguments, meaning more work is needed.

The color ranges thus far observed from various furnaces are:
black, purplish black, greens ranging from pale green to deep green, blues ranging from light blue, dark blue, robins egg blue, to cobalt blue, and carnelian.



Mossy Creek
Mossy Creek Glassy Furnace Slag

This pale blue/green slag is a minority color from the site and was found primarily in the 1903 crib dam fill. The owner states that similar colored slag has been found nearby in road fill.



Mossy Creek
Mossy Creek Glassy Furnace Slag

This dull blue two-tone slag is a minority color from the site and was found primarily in the 1903 crib dam fill. The owner states that similar colored slag has been found nearby in road fill.



Mossy Creek
Mossy Creek Glassy Furnace Slag

This bright blue slag with a much darker blue top is a minority color from the site and was found primarily in the 1903 crib dam fill. The owner states that similar colored slag has been found nearby in road fill.



Mossy Creek
Mossy Creek Glassy Furnace Slag

This medium-deep blue slag is a minority color from the site and was found primarily in the 1903 crib dam fill. The owner states that similar colored slag has been found nearby in road fill.




Forge Slag

The slag on the site recovered and observed to date is from Archibald Cary's Forge operation that ran from 1750 to 1781 when it was burned by Benedict Arnold. Forge slag is bubbly, but it is not glass, although there may be small parts that are glassy. It is primarily composed of charcoal, iron ore, iron prills and silica bodies. At the end of the day, the forge hearths were shut down and upon returning in the morning, the solidified slag in the hearth was removed, placed in a wheelbarrow and carted off to be used as landfill. The bottom of the slag is rounded and was called a skull for the resemblance to a human skull or it was called a mosser because it grew moss on its surface. Either way, picking up a piece of it will result in charcoal coming off on your hand along with rust so you get a black and red hand.

Cary Forge Skull
Cary Forge Skull

Cary Forge Skulls In Situ
Cary Forge Skulls In Situ


Cary Forge Skull Detail
Cary Forge Skull Detail




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