Petty's Run Archaeological Explorations

Cottoning On ……

Back in 1996, as Thomas Edison State College prepared to expand its campus by adding a new wing to the rear of 105-115 West State Street, site preparation work was accompanied by a program of archaeological data recovery.  In the southwestern corner of the site, behind a ten-foot-high retaining wall, archaeologists unearthed the remains of the northeast corner of a substantial stone building, preserved above first-story height.  With the help of deeds, which roughly pinpointed the southwest corner of the Harrow/Yard plating mill, the building corner found on the Thomas Edison State College site was plausibly interpreted as part of this structure, the first water-powered facility on Petty’s Run, built in the early 1730s.

A view in 1996 of the historic foundations uncovered in the southwest corner of the Thomas Edison State College campus during expansion of the college buildings

A close-up view of the building corner found in 1996

For the past 13 years much has been made of the well-preserved state of the plating mill.  Indeed, the mill’s evident survival supplied much of the impetus for the Petty’s Run area being opened up for more expansive exploratory excavation over the past year.  Funny how misguided archaeological interpretation can sometimes be.

The 2008-09 excavations have told a somewhat different story and a round of reinterpretation is now in order.  Deeply buried on the east side of Petty’s Run several different stone foundations have been found, most of which resolve into two separate overlapping building footprints.  A lower, earlier, less well-preserved set of foundations, set slightly at an angle to the line of West State and West Front Streets and not quite perpendicular to the Petty’s Run culvert, is now seen as the remains of the plating mill.  This building footprint does not match up with the corner foundation on the Thomas Edison State College site.  An upper set of foundations, however, does fit well with the corner foundation, giving a building footprint 30 feet square in plan.

  The cotton mill and plating mill foundations to the east of Petty’s Run

The wall in the center, between the box shoring and the middle figure, is now interpreted as the north wall of the cotton mill

So what is this upper set of foundations, of which the corner walls on the Thomas Edison State College property form a part, if it is not the plating mill?  It certainly pre-dates 1849, since it is not shown on a detailed map of the city published in that year.  Revisiting the archival record we now conclude that the upper foundations are the remains of Josiah Fithian’s short-lived and ill-fated cotton mill, one of Trenton’s first textile factories.  Established around 1814-15 and a failed business venture by 1819-20, this mill focused on the carding and spinning of cotton.  It most likely re-used masonry from the plating mill.  The building was still standing in 1822, when it was put up for sale.  We think it was probably demolished in the late 1820s to make way for the Front Street paper mill, which lay immediately adjacent to the south.

  

A sale advertisement for the cotton mill indicating that the building was still standing in 1822

So after all is said and done, we over-optimistic archaeologists must admit that what we originally thought were the mid-18th-century plating mill foundations are in fact remnants of the early 19th-century cotton mill.  This is a fine demonstration of the pleasures and perils of archaeology and the mental challenge that requires us to constantly re-evaluate as we accumulate new data from the ground.  In true scientific manner, we have to develop interpretations that we can test as an excavation unfolds; sometimes they are wrong and need to be revised.

Earthenware Manufacture in a Steel Furnace?

An exceptionally curious outcome of the excavations in the southwestern corner of the Petty’s Run site, in the area where the steel furnace may perhaps have stood, has been the recovery of indisputable evidence of pottery manufacture. On top of and in amongst the stone and brick rubble of the furnace beneath West Front Street we have found numerous sherds of slip-trailed, mottled lead-glazed and black-glazed red earthenware and several items of kiln furniture. Kiln furniture (objects such as sagger fragments, pieces of kiln shelving and props – all of which we have found) is an unequivocal indicator of pottery making. While it is possible that these materials may have originated elsewhere and been indiscriminately dumped at the steel works at the time of its abandonment, their inclusion actually within the same deposit that has produced furnace-related firebrick and metal objects implies that pottery making may have taken place on the site, perhaps even within the furnace. 

Kiln shelving and sagger 

We have no documentary references to 18th- or early 19th-century pottery manufacture occurring on the Trenton Steel Works property, which suggests this may have been a short-lived and informal phase of activity. Archaeologically and stratigraphically, the redware sherds and kiln furniture lie in the upper levels of the furnace debris and are sealed beneath the course of West Front Street. We speculate – admittedly with some timidity and temerity – that between roughly 1785 (when the steel works shut down) and 1792 (when West Front Street was laid out) the steel furnace may have been used for firing pottery. Interestingly, it was during the 1780s and 1790s that members of the McCully family established a redware manufacturing business in Trenton, using several different sites in the downtown, mostly further upstream along Petty’s Run in the vicinity of present-day Bank Street, North Warren Street and Pennington Avenue. Could the McCullys have had an arrangement with the owner of the abandoned steel works site where they could adapt the furnace for pottery making? 

A typical slip-trailed red earthenware pie plate from the McCully pottery in Trenton

Finally a Fix on the Furnace?

As the Petty’s Run archaeological explorations near their conclusion, currently slated for the end of July, the long sought-after steel furnace is slowly coming into focus.  Much of the work over the past month has concentrated on the southwestern corner of the excavation area, immediately adjacent to the southwest corner of the furnace house and extending beneath and to the north of the course of former West Front Street.  Here, ongoing removal of a substantial deposit of stone and brick rubble has produced several blocks of highly fired and heavily glazed mortared brick masonry, a number of large pieces of rough-dressed soapstone (steatite) and some telltale strips of rusted ferrous metal.

View north showing stone and brick rubble deposit adjoining southwest corner of the furnace house

The blocks of brick masonry, some composed of a half dozen or more bricks (most measuring 8.5 by 4 by 2 inches), are presently interpreted as part of the steel furnace structure.  All have been displaced.  The thick greenish-grey glaze covering one face of the bricks, presumably the interior, is thought to be derived from wood fuel used in the firing of the cementation furnace (and perhaps also in an episode of pottery manufacture that may have taken place within the furnace [see following post]).  The soapstone pieces, not native to the immediate Trenton area, are also tentatively seen as part of the furnace structure and were perhaps even used for the stone cementation chest[s], since this rock is known for its insulating and radiant properties.

Block of heavily glazed firebrick, probably from the cementation furnace

The most tantalizing material of all is the ferrous metal, which could be structural iron used in the construction of the steel furnace, or less likely, product from the furnace or forge.  At least three specimens of what we believe are fragments of firegrate bars have been recovered.  The largest specimen is some 10 inches in length.  So what exactly is this material?  Is it wrought iron or cast iron, or could it even be blister steel?  Was it made on site?  Answers must await a more thorough metallurgical examination.

Possible fragments of firegrate bars from the steel furnace

The evidence now being unearthed in the southwestern corner of the site is causing further re-evaluation of the layout of the steel works.  Although by no means certain, we now wonder if the steel furnace adjoined the southwest corner of the 30 by 34-foot furnace house.  If this is correct, the earlier interpretation of the ten-foot square brick platform inside the northeast corner of the furnace house as the base of a water-powered forge may again make more sense.  The final two weeks of excavation will hopefully hold the key; if in-situ structural remains of the furnace emerge beneath the rubble in the southwest corner of the site, this would clinch things ...

What’s in a Ten-Foot Square?

Over the past few weeks, as our June 2 post reveals, the Petty’s Run archaeological team has been pondering the meaning of a ten-foot-square mortared brick and stone masonry platform set within the northeast corner of what is more securely considered to be the “furnace house,” the principal structure of the Trenton Steel Works.  While on June 2 we postulated that this was more likely a forge base than a furnace base, we are still not quite there yet …… not yet ready to commit 100% to this interpretation.


Furnace House and Forge/Furnace Base outlined, looking east, June 1, 2009

In fact, in large part as a result of Ian Burrow communing with other more knowledgeable steel obsessives at the Footprints of Industry conference at Ironbridge a couple of weeks ago, we are almost at the point of reversing ourselves and recognizing the ten-foot-square masonry platform as the base of a single-chest cementation furnace. 

There was a healthy back-and-forth discussion of the interpretive alternatives at the Ironbridge conference.  While everyone agreed that our feature is on the small side, there was both positive and negative evidence pointing to it as a furnace.  On the west and east sides of the square are two very large foundation stones that could form the thresholds of the ash pits that are distinctive features of these furnaces.  The lack of ash and charcoal at our site was not considered an objection, since it was suddenly realized by the group that our furnace, unlike those in England, used wood not coal:  the very high temperatures would reduce the amount of wood ash very considerably.  The patterning of the bricks strongly suggests a central low portion flanked by higher sides, and this could reflect the location of a central chest and chamber, with the furnace walls on either side. 

David Cranstone then referred us to an example noted in Sheffield, England in 1766 by the French metallurgical traveler (and some might say, dastardly industrial spy) Monsieur M. Jars, Correspondant de l’Académie Royales des Sciences de Paris.  David most kindly went to the trouble of furnishing us with Jars’ published account of 1774 describing his observations of steelmaking in Sheffield and elsewhere in northern Europe.  Jars’ furnace image certainly has similarities of scale and form to our foundation.

Cross-sections through a steel furnace in Sheffield, England recorded by M. Jars in the 1760s

So today, we lean toward our ten-foot square being the base of a steel furnace.  Tomorrow, who knows.  Part of the problem here is that one critical, poorly understood portion of the site, southwest of the furnace house, is still under excavation and may yet hold a surprise or two.  No matter, all will be revealed in due course.  All the best archaeological endeavors pass through these phases of confusion and heightened suspense (and occasional low anticlimax) as the worthy process of excavation plumbs the depths of history.

A Most Valuable Conference Experience.

2009 is not only the year in which Trenton’s 18th-century steel furnace was uncovered (important though we are sure that is).  It also marks an important anniversary in industrial history.  In 1709, Quaker Ironmaster Abraham Darby successfully and profitably produced iron from a blast furnace by using coke, rather than coal or wood, as the fuel.  He did this in a valley called Coalbrookdale on the River Severn in Shropshire, in the West Midlands of England.


The late 18th-century Bedlam blast furnaces in Ironbridge Gorge

Today Coalbrookdale and the adjacent Ironbridge Gorge (named for the world’s first wrought iron bridge, built across the Severn in 1781) are a World Heritage Site commemorating the Industrial Revolution.  The area is now home to six outstanding industrial museums (photo) and to numerous preserved industrial historic sites (photo).  

The Ironbridge Gorge Museum complex where the “Footprints of Industry” conference took place

From June 3 to June 7 a conference (“Footprints of Industry”) was held here to celebrate Mr. Darby’s achievement.  As explained on June 4, Ian Burrow had the privilege of addressing the conference with a preliminary report (written by Richard Hunter and Ian) on the history and archaeology of the Trenton Steel Works.

It was our great good fortune that the conference was attended by some of the leading authorities on the early steel industry in the United Kingdom.  Paul Belford of the Ironbridge Gorge Museum Trust and Ronald Ross of Wilfred Laurier University in Ontario, Canada are the excavators of two Coalbrookdale cementation furnaces dating to the early 17th century.  David Cranstone is well known in British industrial archaeology for (among other things) his magisterial study of the famous preserved 18th-century cementation furnace at Derwentcote in northeastern England.  David Dungworth of English Heritage is an expert on the analysis of slag and other debris from these sites and wringing historical and information out of such superficially unappetizing material.  Peter King has spent many years researching the history of the iron industry in England and Wales and has published numerous papers on the subject.

These gentlemen generously shared their knowledge of, and enthusiasm for, all things steel.  Their numerous comments and insights into our Trenton data were extremely helpful, and will inform our future journal entries.  All that need be said here is that this was scholarly interchange at its very best, and that there is an international dimension to the Trenton Steel Works site that we are only now fully beginning to realize. 

Burrow in Full Blast.

Tomorrow, June 5, 2009, at 3.00 p.m. GMT, Ian Burrow will be delivering a paper, co-authored with Richard Hunter and entitled “Steel Away: The Trenton Steel Works and the Struggle for American Manufacturing Independence in the Eighteenth Century,” at the Fe09 Footprints of Industry Conference (300 Coalbrookdale 1709-2009) jointly organized by the Society for Post-Medieval Archaeology, the Historical Metallurgy Society, the Association for Industrial Archaeology and the Newcomen Society and being held at the Coalbrookdale complex in the Ironbridge Gorge, Shropshire, England.  This event celebrates the 300th anniversary of the first commercial use of coke to smelt iron.  All involved with the Petty’s Run excavations wish Ian well in his efforts at communicating their abiding interest in the Trenton Steel Works with archaeological colleagues in the metal motherland.

Ian Burrow digs paper

A Revealing Advertisement.

In attempting to make sense of the unfolding field evidence, archaeologists continually pore over contemporary documents.  For the Trenton Steel Works, numerous sale advertisements, like the one transcribed below, provide key snippets of information that help to frame the jigsaw puzzle of the site and guide interpretive thinking.

The Pennsylvania Gazette, No. 1914, August 29, 1765

To be sold by publick Vendue, at the London Coffee house, at Six o’Clock in the Evening, on Saturday, the 14th of September, One half Part of the Steel Works at Trenton, with a Lot of Land belonging thereunto, containing nearly Half an Acre, with a Smith’s Shop, which hath one Fire-place; the House which contains the Furnace is built with Stone, and almost new, large and commodious, being 30 by 34 Feet square.  The Situation of the above Works gives it an advantage over any in the Colonies, being in a County where Wood may be had cheap in great Plenty, and at the Head of the Tide Water, where they can receive Iron from a Number of Iron-works which are situate above it on Delaware; they can likewise transport by Water the Steel to Philadelphia, or any other Part, at a moderate Expence.  An Inventory of Movables, &c. belonging to the Works, will be exhibited on the Day of Sale.  For further Information, apply to OWEN BIDDLE

It’s a steel ….

Is it a furnace?  Is it a forge?  Was it water-powered, or was its position close to the creek purely fortuitous?  These and numerous other questions have been consuming the archaeologists excavating 18th-century levels at the Petty’s Run site over the past month or more.  Gradually, as the 19th-century features have been unraveled, foundations and soil layers associated with colonial and still earlier Native American land use have been revealed.  Day by day, with the help of documents, background reading, and advice from colleagues around the globe, the archaeology is being interpreted with growing confidence.

Traces of the furnace house and a forge base at the Trenton Steel Works emerge from beneath the remains of the paper mill

As of the end of May, a patchwork of rough-dressed stone foundations with a distinctive orange clayey mortar has been delineated beneath and around the 19th-century paper mill to the west and northwest of its wheel pit.  Through careful measurement a building outline corresponding to what is referred to in documents as the “furnace house” is now recognized.  A sale advertisement from 1765 describes this structure as being 30 by 34 feet in plan.  The building is ranged east-west to the west of Petty’s Run, but has other structural elements extending both eastward, that are cut through by the paper mill wheel pit, and westward, that continue beyond the current limit of the excavation.

View of the stone and brick base of the finery forge overlaid by the north wall of the paper mill

Set within the northeastern corner of the furnace house footprint is a massive stone and brick platform-like foundation, roughly ten feet square in plan and showing some evidence of intense heat in the center.  When first encountered, this was considered possible evidence of the furnace structure, even though several things did not add up.  Where were the flues and ash pit?  Where were the firebrick and refractory stone and burned sand and crozzle that one would expect to find on the site of a furnace?  Prompted by challenging questions from colleagues, and following review of other 18th-century iron and steel working sites, a more carefully considered interpretation now sees the ten-foot-square platform as the base of a hearth of a large forge.

 
A sketch of a finery forge in Wales made by Reinhold Rucker Angerstein while traveling in Britain in June of 1754

Upon still more rigorous examination of its masonry, the forge base was observed as having two-foot-wide walls along its northern and southern sides with a tightly laid brick floor in between and matching stone slabs centrally placed at its eastern and western ends.  Currently we postulate that the forge made use of one or a pair of water-powered bellows breathing air into the hearth from its southern side.  Under this scenario the waterwheel would have been located immediately east of the furnace house in roughly the same spot as the later paper mill wheel pit.  Hypothesized to be a finery forge carrying out secondary processing of steel (and perhaps also bar iron), this may correlate with what is described as a “smith’s shop” in the sale advertisement of 1765.

Of Wheels and Turbines.

Finally, the riddle of the paper mill wheel pit is solved – well, mostly.  After some serious mastication on the meaning of certain timber and iron remains, and with the help of a few choice documentary references, a reasonably water-tight theory of the sequence of use and modification of the wheel pit may now be floated.  The final period of use of the wheel pit, from the late 1860s up until 1876, when the paper mill ceased operation and was pulled down to make way for row housing, involved a water turbine.  The vast majority of the timber and iron contents recovered from the wheel pit relate to this turbine phase.


Looking upstream, in the foreground in front of the scale pole, part of the base of the main water box for the turbine; beyond, the base of the adjoining compartment, also water-filled, that served as a fore-chamber for the water box

The turbine, probably around four feet in diameter, operated within the lower part of a large wooden box, roughly five by six feet in plan and at least nine feet deep.  Adjoining on the upstream side was a large wooden compartment, seven feet by three feet at the base and of similar nine-foot depth, braced with iron tie rods.  Although only the bottom of this compartment survived, its upstream wall sloped upward and is projected to have been perhaps seven feet square at the top.  We think this compartment served as a sort of stilling basin, providing a steady, turbulence-free flow of water into the turbine in the water box.  The turbine would have operated underwater, suspended in a floor three to four feet above the wheel pit base and functioning like a plug in a sink through which water flowed, generating power.  One problem:  the industrial census return for 1870 records the paper mill as having two turbines.  Were there two turbines somehow arrayed in the water box?


The fore-chamber compartment partially disassembled

A mechanic’s lien filed with Mercer County in 1866 gives us another benchmark in understanding the wheel pit.  In this year, Trenton builder Edmund Craft placed a lien on Horatio Armstrong’s assets for Armstrong’s non-payment of bills for construction work at the paper mill.  From the wording of the lien, it appears the mill underwent a major rebuild between May of 1865 and May of 1866.  At this time the mill contained “one cast iron water wheel and all the gearing shafting and fixtures connected ….”  Based on this reference, we infer that in 1865 a cast iron wheel was installed in the wheel pit, and was in use for only a few years between 1865 and the time the turbine[s] was installed prior to 1870.  Along with the cast iron wheel, we believe that the wheel pit’s finely dressed stone side walls were installed within an earlier wheel pit chamber in 1865-66.  Based on the bearing slots in the side walls the cast iron wheel (probably assembled from pre-cast members and wood parts) is calculated to have been 20 feet in diameter and perhaps six to eight feet in width.  The plank floor that extends across the wheel pit beneath the fore-chamber compartment probably dates from 1865-66.


Looking downstream, the base of the fore-chamber and turbine water box; tail waters flowed out of the wheel pit over exposed bedrock at the upper left

The original, pre-1865 wheel pit is thought to lie behind the dressed stone side walls and is estimated to have been 11 to 12 feet wide.  Traces of a bearing slot on the west side imply that it also contained a 20-foot-diameter wheel.  The wheel pit’s downstream wall probably remained the same throughout the history of the paper mill.  The fact that mortar is washed out of its upper courses may indicate that the wheel was overshot.  The pit’s upstream wall is carved out of solid bedrock.

Reslabbing the Culvert.

At the top of the bluff, just downstream of the manhole that gives access into the Petty’s Run culvert, is a series of four massive stone slabs that formerly carried a backyard alley over the stream in the late 19th century.  These slabs rest on steel I-beams laid across the culvert sidewalls.  When studied in detail last year, one of the slabs was cracked, the beams were severely corroded and there was a real danger of the culvert roof collapsing.  A couple of weeks ago, Steve Spaulding, with the help of expert Italian-American mason Angelo Cantillo, carried out a surgical repair of this capping of the culvert.  The slabs were removed, the rusted beams were replaced with new steel members, portions of the stone and brick masonry were re-laid and re-pointed, and the slabs were then re-set and cemented.  Voilà!  This particular spot along the course of the culvert is now safe to stand on and available to the park designers as a potential viewing platform within the site.

Removing slabs for the culvert repair

The culvert, sealed and repaired