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Craft & Industries: Ferrous Metal-Working

Catherine Mortimer

Metalworking debris was recovered from contexts dating from the Roman to the medieval period. At Blue Bridge Lane, 746 small finds of metalworking waste were recovered, weighing just over 40kg in total. Most of these samples are small, 656 of them weigh less than 100g, and 120 are tiny 'hammerscale' samples retrieved from environmental sieving. Fishergate House is a smaller site with 50 small finds of metalworking waste, totalling just over 5kg, with one of the samples (Find no 868) weighing more than 2kg. As the two sites are close, they are considered here together.

Material classification

The material was classified, as far as possible, based mainly on appearance and density (Table 1 and catalogues). The majority of the material is ironworking debris. Eight examples of smithing hearth bottoms ('shb' in table) were noted (Find nos 330, 5084, 5177, 5221, 5222, 5271, 5277 and 5279) at Blue Bridge Lane; none were found at Fishergate House. Smithing hearth bottoms are large pieces of slag formed in the high temperatures of a smithing hearth by the combination of iron compounds, silica and fluxes (in the form of ashes). The classic shape is plano-convex, with a curved base and roughly flat upper surface. At Blue Bridge Lane, the smithing hearth bottoms have an average weight of 455g, and are about 100mm wide, at the widest, and about 50mm deep. These sizes are comparable to contemporary examples at Coppergate and Fishergate (McDonnell 1992, 1993).

Smithing slag is often found in more irregular-shaped lumps. These are evidence for a smithing hearth bottom having been broken up, or often simply indicate that the slag never coalesced into a complete smithing hearth bottom. Some of this can be classed as smithing slag lumps ('ssl' in table), but much of the rest of the slag cannot be characterised, apart from being ironworking slag ('slag' in table); the majority of the debris at both sites was classed under these two headings (60% at Blue Bridge Lane and 90% at Fishergate House). About 80% of the undiagnostic 'slag' samples are small, less than 100g, making further comment difficult. Where samples were mixed and the material was fragmentary, it was impractical to subdivide it and the sample was assigned to the most common material i.e where slag/vfl, the weight was given to 'slag'. Much of this is also likely to be from smithing; no evidence diagnostic of iron smelting was detected amongst the samples. Although some of the slag samples were notably denser and more 'ropey', this could have arisen accidentally during smithing.

Both spherical and flake hammerscale were observed among the samples, although some of the 'hammerscale' samples are in relatively chunky shapes and is probably actually from decaying, rusted artefacts. Hammerscale is produced during ironworking, typically when tiny droplets are driven from iron billets during initial shaping (spherical hammerscale) or when flakes come off objects during final shaping (flake hammerscale). The hammerscale was not examined in detail.

Fired and vitrified clay may come from ironworking hearths or other high-temperature working. The fired clay material at Blue Bridge Lane includes a well-preserved tuyère (Find no 6233), which is vitrified on one side and oxidised on the other. The once-central hole has a diameter of about 15mm. It is possible that the tuyère may have been made of two pieces of clay, as there seems to be a prepared surface running radially from the central hole. Another ceramic item (Find no 2832) remains unidentified. It is small, weighing 11g, with a 43mm maximum dimension, reduced-fired, with thin (5mm) walls and has an enclosed, possibly triangular shape. Inside there is a dark deposit. It is a curious shape for a mould, and if it is a mould, must have been from an investment mould. There are some other possibilities, including precious metal processing or assaying (based in the dark deposit).


Tuyère, artefact 6233	Tuyère, artefact 6233

Under the category of 'other' a variety of material types were recorded. Occasional small pieces of iron object, possibly offcuts from production, were observed within the samples. Two pieces of copper alloy waste were recorded from Blue Bridge Lane (Find nos 4605 and 5049), indicating a very low level of copper-alloy working or, more likely, accidental loss. Find no 323 comprises some smithing slag and a large lump (173g) of glassworking waste. This latter is a small piece of dense, reduced fired clay material (probably crucible), with thick layers of green-ish glass and white, quartz-rich material attached. This certainly appears to be post-medieval in date, on a typological basis, and may well have come from the Redfearn glass factory, active at the neighbouring Fishergate site from the 18th to the 20th century.

Table 1. Summary of slag assemblage
	BBL	FH
	Wt (g)
Smithing hearth bottoms	3638	-
Smithing slag lumps	14909	2122
Ironworking slag	14176	2513
Vitrified hearth lining	2192	399
Fired clay	1882	26
Other	1094	39
Total	37891	5099

NB these weights do not include hammerscale samples which were too small to weigh.

Dates

At Blue Bridge Lane, the majority of the debris comes from Period 3 contexts, with lesser, but significant quantities from Period 8 contexts. The Period 3 material includes seven of the smithing hearth bottoms, as well as the largest amounts of all of the other material types, with the exception of fired clay which was more common in Period 8. It is notable that the tuyère and the majority of the leadworking evidence were also found in Period 3. A relatively large lump of copper alloy waste (Find no 5049) was found in a Period 6 context. The mystery fired clay object and the glass waste (Find no 2832 and 323) come from undated contexts.

Table 2. Distribution of waste, by period at Blue Bridge Lane
	2	3	6	7	8	9	UD
	Weight (g) by period
Smithing hearth bottoms		3162					476
Smithing slag lumps		9193	308	536	2166		2706
Ironworking slag	412	7383	1520	1053	2223	245	1390
Vitrified hearth lining	8	1095	107	108	621	12	265
Fired clay		440	14	173	900	88	454
Other		135	120	57	68	72	528
Total	420	21411	2069	1927	5978	417	5819

Distribution

It is difficult to see a significant distribution pattern for the ironworking at Blue Bridge Lane. The features containing Period 3 and Period 8 slag are scattered widely throughout the excavated area.

Comparison with other sites

The metalworking debris at these sites is of a typical type and of a moderate quantity for urban sites. Clearly ironworking was going on relatively close by, during several periods of activity but all of the debris is redeposited, with no in situ structural evidence for metalworking furnaces/hearths at the site. The overall quantities of debris recovered (45kg) can be seen as relatively small, compared with various sites in York (excavated areas/volumes vary);

Coppergate	248kg	Roman, Anglo-Scan to medieval (McDonnell 1992)
Fishergate	172kg	Anglo-Scan to medieval (McDonnell 1993)
Walmgate	138kg	medieval and late-medieval (MacNab 2003)
St Andrewgate	94.5kg	medieval and late medieval (Finlayson 2004)

Although Anglian deposits at Blue Bridge Lane produced about a third of the quantity of debris found in contemporary contexts at Fishergate, ironsmithing slag was the dominant material in both studies (83% Fishergate and 92% at Blue Bridge Lane), with lesser amounts of fired clay and vitrified clay. However, there is only a small amount of evidence for other forms of metalworking at Blue Bridge Lane, whereas at Fishergate, a range of debris shows that several other metalworking techniques were used; specifically, copper and silver alloys were melted, and non-ferrous wire and sheet items were worked. Similarly, at Coppergate, ironworking was carried out alongside an important silver-working industry, and there is evidence for melting and casting a range of non-ferrous metals, as well as precious metal refining.

Codes for Tables

fc fired clay
Fe iron
fl hs flake hammerscale
hs hammerscale
magn magnetic
shb smithing hearth bottom (weight (g), width and depth (mm) given, where possible)
sph hs spherical hammerscale
ssl smithing slag lumps
vhl vitrified hearth lining

Catalogue
Find	Feature		Spot Date	Description of Context	Weight (g)	Identification
323		1022		Secondary Layer	434	250g ssl, 173g glass waste
326	4	1029		Secondary Backfill of Robber Pit	66	ssl
330	13	1063		Secondary Backfill of Pit	538	shb
331	4	1028	Med 11th to 12th	Secondary Backfill of Robber Pit	376	ssl
332	13	1027		Secondary Recovery Context from Pit	540	ssl (two lumps)
2832			Med	Backfill of terracing cut	11	?mould ?other mworking
2833			Late Med	Backfill of Scoop	12	soft-fired white clay, not mworking
5011		1221	E mod	Secondary Garden Soil Layer	110	fc (over-fired)
5012		1227	19th+	Secondary Garden Soil Layer	524	ssl (one large lump)
5046		1385	Med 14th+	Buried Soil	1264	ssl (mostly one big lump)
5071	353	1449	Asax	Secondary Backfill of Pit	702	ssl (many small lumps)
5084	225	1491	Med 14th+	Secondary Backfill of Kiln	486	386g shb, w= 105, d = 45)
5088	226	1492	Med 14th+	Secondary Backfill of Posthole	452	ssl
5096	239	1514	?Pmed L15th+	Secondary Backfill of Pit	966	ssl
5126	269	1592	Med 12th to 13th+	Secondary Backfill of Pit	122	charcoal
5161	303	1677		Backfill of Pit	420	ssl or shb?
5177	321	1707		Secondary Backfill of Posthole	476	shb (1 example, w=105, d = 42)
5185	77	1743	Med 13th to14th+	Primary Fill of Pit	1352	ssl mostly, plus 152g vhl
5218	381	1851	Asax	Secondary Backfill of Pit	390	284g = ssl, 22g = fc, 65g = wattle
5221	381	1858	Roman	Primary Fill of Pit	588	shb (1 example, w=130, d = 65)
5222	381	1861	Med 12th+	Recovery Context from Pit	614	389g = shb (w = 100, d = 40) plus ssl
5228	402	1883	Asax	Secondary Backfill of Pit	508	ssl and shb?
5245	442	1951	Asax / Med 13th+	Primary Backfill of Pit	1264	ssl, vhl (small chunks)
5246	442	1951	Asax / Med 13th+	Primary Backfill of Pit	1822	ssl (large chunks)
5251	458	1969	Med 14th+	Secondary Backfill of Pit	350	ssl, mostly small
5261	442	2024		Secondary Backfill of Pit	1532	ssl
5271	381	2054	Roman L2nd+	Secondary Dump in Pit	632	shb (1 example w = 110, d = 75), including Fe-rich item
5289	273	2103	Roman	Secondary Backfill of Pit	498	ssl (one large lump)
5308	4	H. scale 1006	Med 12th+	Secondary Backfill of Robber Pit	<1	magn debris and fl hs
5332	13	1147	Asax	Secondary Fill of Pit	6	vhl
5348		H. scale 1286		Seconadry Spread of Soil and Tile Deposit	4	sph hs, fl hs and magn debris
5359		H. scale 1331	Med 13th-14th	Secondary Layer sealing Feature 164	<1	magn debris
5363	150	H. scale 1334	Med 11th to 12th	Secondary Backfill of Pit	4	vhl
5367	178	H. scale 1336	Med 13th	Secondary Backfill of Scoop	<1	magn debris and ?sph hs
5372	150	H. scale 1339	Med 11th+	Primary Fill of Pit	<1	magn debris, sph hs and fl hs
5410	215	1435	Med 14th+	Secondary Backfill of Pit	8	vhl
5417	198	H. scale 1442	Med 14th+	Primary Backfill of Pit	<1	fc
5426	223	H. scale 1484	Med 12th / 14th+	Secondary Backfill of Pit	4	sph hs, fl hs and magn debris
5440	218	1515	Med 12th to 13th	Primary Fill of Pit	<1	vhl
5465	143	H. scale 1534		Secondary Backfill of Pit	<1	magn debris and sph hs
5468		H. scale 1541	Med 12th to 13th	Secondary layer	4	magn debris and sph hs
5516	351	H. scale 1763	Med 11th+	Fill of Pit	6	sph hs, fl hs and magn debris
5576	13	1908	Roman	Fill of Pit	14	dense slag and vhl
5578	397	H scale 1909		Primary Fill of Pit	<1	mag deb and fl hs
5595	458	H. scale 1973	Asax / Med 13th+	Primary Fill of Pit	6	magn debris and ?fl hs
5599	458	H. scale 1974		Primary Fill of Pit	4	magn debris
5679	546	H. scale 2195	'Roman / Med 14th+	Primary Fill of Pit	4	magn debris and sph hs
5688		H. scale 2205	Roman ?1st to 2nd	Secondary Layer	4	magn debris and sph hs
6085	241	H. scale 1517	Asax	Primary Backfill of Pit	<1	magn debris and fl hs
6233			Asax	Backfill of Pit	82	tuyere