38:
31:
418:. The heat transfer through the clay has to be sufficiently high to heat up the air passing through the clay chamber, in order to achieve a higher temperature in the blast zone, which in turns leads to more heat transfer through the clay walls of the tuyère. Many small pieces of tuyère with physical characteristics indicating their presence inside furnaces were recovered at the KM2 site. The majority of tuyère fragments show convincing evidence in their colors to indicate that they were inside the prehistoric smelting furnaces of KM2.
536:
70:
391:
than the KM2 furnace pits. The furnace bowls are larger and more regular in size than the KM2 furnaces, with a mean diameter of 113.8 cm (44.8 in), ranging only between 112–116 cm (44–46 in). The mean depth of 28 cm (11 in) among KM3 furnace pits is significantly greater than the mean depth of 18 cm (7.1 in) at KM2, a difference attributable to the more complete preservation at KM3.
488:
operation of the furnace. Later metallurgical analysis of the iron bloom shows evidence that the piece of iron had been produced by a smelting process that had formed large, dense, relatively slag-free bloom. The placement of this unprocessed iron in the pit evokes ethnographic comparison to iron smelting rituals that ensure the production of high-quality iron that mimics the attribute of the ritual device.
295:. At the KM2 and KM3 sites, Schmidt tested the hypothesis that the high combustion temperature of furnaces, discovered to be between 1,350–1,400 °C (2,460–2,550 °F), was caused by the preheating of air blasts. Preheating has been suggested to be a distinct feature of African Early Iron Age smelting techniques by ethnographic observations of the
478:
Of the 15 furnace bowls excavated at the KM2 site, six had a small hole in the floor. Ethnographic evidence suggests that iron smelters excavated holes in their furnaces in order to place in it magical devices or ritual medicine. Sometimes these ritual objects were used to increase productivity or to
378:
and the furnace shaft was built with bricks. The furnaces have a mean diameter of 93.6 cm (36.9 in), ranging between 86–103 cm (34–41 in) in diameter, with 10 of the 11 furnaces between 93–103 cm (37–41 in). In KM2, large amounts of industrial debris and domestic pottery
421:
The hypothesis that preheating had developed at least by the 400 AD in Africa has been confirmed by the discovery of a 36 cm (14 in) whole or long section of tuyère uncovered in furnace 9 of KM3. The tuyère is 40% (14.5 cm (5.7 in)) slag-wetted and vitrified, and the slag-wetted
390:
At the KM3 site are mines, slag dumps, ore-processing areas, industrial refuse dumps, and smelting furnaces. Smelting furnaces were abundant, although recent farming practices in the core of the industrial site had disturbed some furnaces. The KM3 furnaces are more consistent in design and contents
357:
and 250 AD); the second during 300 AD, when iron production was performed only in one episode at KM3 and was totally absent at KM2; and the third in 400-500 AD, which was also an active period at KM2, but the end of iron smelting at KM3. During the last use period of KM2 in the 600-700 AD, KM3 site
460:
60% of the KM2 furnaces were lined with termite earth, but only one of the KM3 furnaces had traces of an artificial liner. It is uncertain if furnace liners were not as common at KM3 or if they had been removed from furnaces. The earth of a termite mound is more refractory than normal soil because
345:
in the deeper stratigraphic zones of the furnace pits. The KM2 radiocarbon dates show that there are 4 distinct use periods of the site: the first is an occupation period that spans from 300 to 200 BC; the second is an industrial period in 100-200 AD, after which there is a hiatus from 200-300 AD;
446:
in
Northwestern Tanzania shows that swamp grass is burned in the furnace bowl until the bowl is filled with the charred swamp reeds. When the iron ore melts above the tuyères, it forms a molten slag with carbon inclusions. The slag then interacts with the fibrous, carbonaceous bed provided by the
410:
Preheating of air blasts allowed the furnaces to achieve higher combustion temperatures, which dramatically improved fuel efficiency in the iron production process. Peter
Schmidt observed that the Haya in northwestern Tanzania employed the practice of preheating by placing tuyères inside their
487:
Of the seven furnaces excavated at KM3, only furnace number 8, dated to 100 AD, has shown evidence of ritual modification. In the furnace floor, a small pit was discovered that contained a 6-cm-tall piece of prehistoric iron bloom, which was shown to have no relationship to the technological
324:
The KM3 site is situated 1 km (0.62 mi) south of KM2 and sits 75–85 m (246–279 ft) above Lake
Victoria. It was discovered during a village survey by a Tanzanian surveyor, who observed furnace bricks on a main path bisecting the site.
411:
furnaces, which results in hot air blast. The study of KM2 and KM3 sites allowed for the collection of more definitive evidence for prehistoric tuyères, in order to discern how and when preheated iron technology developed in Africa.
349:
All 10 dates of KM3 site are derived from furnace pits. The dates show that there are three use periods at the KM3 site: the first period is represented by two contiguous furnaces that are dated to the 100-200 AD (or between
517:
451:
of the bloom. The charred reeds also allow the draining of slag from the blast zone, as the slag runs down the inside of the grass stalks and through the spaces between the reeds to the bottom of the furnace pit.
320:
port facility. It was discovered in early 1977 by a
Tanzanian member of Peter Schmidt's team as he walked over a newly exposed road surface that had been opened as part of the new Kemondo Bay port access road.
426:. Other physical properties of the tuyère, such as the reduction of clay, also suggest that tuyères had been placed inside Early Iron Age furnaces for the preheating of air blast.
265:
524:
479:
protect against sinister forces that might disrupt the smelt. The properties of the ritual materials are those that the smelters hoped to impart to the iron bloom.
1162:
Schmidt, Peter R.; Childs, S. Terry (1985). "Innovation and
Industry during the Early Iron Age in East Africa: The KM2 and KM3 Sites of Northwest Tanzania".
502:
1315:
435:
439:
317:
510:
371:
95:
1325:
1330:
1320:
1305:
532:
394:
The furnace bowls excavated on KM2 and KM3 were filled with a variety of materials, including slag, pieces of partly reduced
540:
497:
220:
465:
to build their mounds. Termite mound soil is used as insulation, and employed for its resistance to fusion with slag.
1335:
1284:
1259:
1310:
1206:
Schmidt, Peter R.; Avery, D. H. (1983). "More
Evidence for an Advanced Prehistoric Iron Technology in Africa".
855:
30:
284:
176:
447:
burned swamp grass, which in turn provides an extremely high carbon-slag contact area for the subsequent
1102:
Schmidt, Peter; Avery, Donald H. (1978). "Complex Iron
Smelting and Prehistoric Culture in Tanzania".
346:
the third in the 400-500 AD; and the fourth falls from the beginning of 600 AD into early 700 AD.
873:
640:
438:
tend to be cleared out after smelting, this serves as the most direct evidence for the use of
617:
269:
57:
1076:
591:
8:
957:
921:
767:
622:
1223:
1179:
1119:
1023:
998:
980:
939:
832:
721:
571:
1280:
1255:
1127:
1046:
1013:
1003:
711:
414:
The tuyères employed inside the smelting furnace must be made of clay that is highly
1215:
1171:
1111:
729:
334:
1115:
434:
A small pile of charred reeds was found adjacent to furnace 3 in KM2, and since
1219:
837:
777:
747:
599:
367:
287:
in the late 1970s and 1980s. The excavations aimed at better understanding the
261:
143:
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988:
891:
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762:
698:
660:
632:
609:
556:
548:
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375:
313:
288:
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273:
110:
97:
62:
1131:
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896:
883:
847:
814:
739:
1031:
970:
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757:
688:
443:
296:
292:
153:
1183:
1175:
1123:
947:
650:
576:
415:
1227:
803:
678:
423:
399:
1252:
Iron
Technology in East Africa: Symbolism, Science, and Archaeology
1051:
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683:
673:
566:
535:
395:
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338:
277:
75:
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were dumped into a refuse pit alongside discarded furnace bricks,
929:
901:
752:
645:
561:
462:
374:
and iron artifacts. The furnace bowls were lined with earth from
202:
Antiquities
Division, Ministry of Natural Resources and Tourism
1008:
581:
398:, fired bricks used to build the furnace, charcoal, pieces of
993:
906:
827:
706:
380:
342:
442:
in the iron production process. Ethnographic study of the
1277:
The
Culture & Technology of African Iron Production
370:
furnaces were excavated along with a large industrial
1254:. Bloomington, Indiana: Indiana University Press.
316:on a knoll 500 m (1,600 ft) west of the
422:section is gray in color, suggesting exposure to
312:KM2 site is located 14 m (46 ft) above
1297:
366:In KM2, the bases of 13 intact and 2 disturbed
37:
1161:
518:
1279:. Gainesville: University Press of Florida.
1205:
1101:
461:termites select quartz sand grains from the
525:
511:
337:from the KM2 site are derived from wood
1316:8th-century disestablishments in Africa
1274:
1249:
1298:
506:
328:
1245:
1243:
1241:
1239:
1237:
1201:
1199:
1197:
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1153:
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1149:
1147:
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1143:
1141:
1097:
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402:, as well as some domestic pottery.
541:National Historic Sites of Tanzania
498:National Historic Sites in Tanzania
221:National Historic Sites of Tanzania
13:
468:
455:
361:
358:was not used for iron production.
291:process and its ritual aspects in
16:National Historic Site of Tanzania
14:
1347:
1234:
1190:
1164:The African Archaeological Review
1138:
1090:
1326:Archaeological sites in Tanzania
534:
473:
341:found beneath furnace bricks or
68:
36:
29:
1331:Industrial archaeological sites
1321:1977 archaeological discoveries
1275:Schmidt, Peter R., ed. (1996).
383:, tuyères, iron fragments, and
266:industrial archaeological sites
1268:
1069:
856:Kalambo Falls Prehistoric Site
429:
302:
1:
1306:3rd-century BC establishments
1116:10.1126/science.201.4361.1085
482:
351:
280:, excavated by a team led by
1208:Journal of Field Archaeology
307:
7:
491:
10:
1352:
1250:Schmidt, Peter R. (1997).
1220:10.1179/009346983791504228
405:
299:of northwestern Tanzania.
1022:
979:
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126:
89:
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53:
45:Site location in Tanzania
24:
1336:Iron Age sites in Africa
1063:
1311:700s disestablishments
1077:"Antiquities Division"
641:Isimila Stone Age Site
254:Kemondo Iron Age Sites
231:Kemondo Iron Age Sites
20:Kemondo Iron Age Sites
958:Zanzibar South Region
922:Zanzibar North Region
270:Bukoba Rural District
165:Excavation dates
58:Bukoba Rural District
592:Dar es Salaam Region
194:Tanzanian Government
111:1.45806°S 31.77444°E
1110:(4361): 1085–1089.
874:Livingstone's Tembe
768:Lindi Historic Town
623:Bahi Rock-Art Sites
107: /
21:
1176:10.1007/bf01117455
1024:Pemba South Region
981:Pemba North Region
833:Chole Island Ruins
722:Kilimanjaro Region
572:Nasera Rockshelter
329:Radiocardon dating
207:Public access
116:-1.45806; 31.77444
19:
1060:
1059:
1047:Ras Mkumbuu Ruins
1014:Kichokochwe Ruins
712:Uvinza Salt Works
669:KM2 and KM3 sites
355: 50 BC
335:radiocarbon dates
268:in Kemondo ward,
251:
250:
168:1970s & 1980s
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730:Marangu Defences
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1018:
999:Mkia wa Ng'ombe
975:
952:
934:
916:
878:
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842:
809:
790:
772:
734:
716:
693:
655:
627:
604:
586:
543:
533:
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494:
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476:
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469:Ritual medicine
458:
456:Termite linings
432:
408:
364:
362:Iron technology
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1318:
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1308:
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1214:(4): 421–434.
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838:Kisimani Mafia
835:
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819:
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811:
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778:Manyara Region
774:
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748:Kilwa Kisiwani
744:
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600:Kunduchi Ruins
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376:termite mounds
368:Early Iron Age
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262:Early Iron Age
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173:Archaeologists
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144:Early Iron Age
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85:Eastern Africa
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15:
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1286:0-8130-1384-4
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1261:0-253-21109-3
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940:Zanzibar West
937:
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928:
927:
925:
923:
919:
913:
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905:
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892:Tongoni Ruins
890:
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871:
869:
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866:Tabora Region
863:
857:
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845:
839:
836:
834:
831:
829:
826:
824:
821:
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806:Historic Town
805:
802:
801:
799:
797:
796:Mtwara Region
793:
787:
784:
783:
781:
779:
775:
769:
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764:
763:Sanje ya Kati
761:
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731:
728:
727:
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723:
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699:Kigoma Region
696:
690:
687:
685:
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677:
675:
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664:
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661:Kagera Region
658:
652:
649:
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642:
639:
638:
636:
634:
633:Iringa Region
630:
624:
621:
619:
616:
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610:Dodoma Region
607:
601:
598:
597:
595:
593:
589:
583:
580:
578:
575:
573:
570:
568:
565:
563:
560:
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557:Olduvai Gorge
555:
554:
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549:Arusha Region
546:
542:
537:
528:
523:
521:
516:
514:
509:
508:
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489:
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474:Furnace holes
466:
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453:
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449:carburization
445:
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436:furnace bowls
427:
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314:Lake Victoria
300:
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289:iron smelting
286:
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282:archaeologist
279:
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274:Kagera Region
271:
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228:Official name
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177:Peter Schmidt
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63:Kagera Region
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56:
52:
32:
23:
1276:
1270:
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1211:
1207:
1167:
1163:
1107:
1103:
1080:. Retrieved
1071:
1037:Pujini Ruins
912:Yambe Island
897:Toten Island
884:Tanga Region
848:Rukwa Region
815:Pwani Region
740:Lindi Region
668:
486:
477:
459:
433:
420:
413:
409:
393:
389:
365:
348:
332:
323:
311:
285:Peter Schmid
257:
253:
252:
1032:Mkama Ndume
1004:Msuka Mjini
971:Kuumbi Cave
966:Unguja Ukuu
828:Kaole Ruins
758:Songo Mnara
689:Bweranyange
444:Haya people
440:swamp grass
430:Swamp grass
318:Kemondo Bay
303:Description
297:Haya people
293:East Africa
258:KM2 and KM3
114: /
90:Coordinates
1300:Categories
651:Mlambalasi
577:Mumba Cave
483:Iron bloom
416:refractory
372:refuse pit
199:Management
160:Site notes
130:settlement
102:31°46′28″E
1170:: 53–94.
948:Stonetown
804:Mikindani
679:Nyabusora
424:oxidation
308:Locations
191:Ownership
186:Excavated
183:Condition
99:1°27′29″S
1184:25130450
1132:17830304
1052:Shamiani
1042:Chambani
823:Bagamoyo
786:Luxmanda
684:Katuruka
674:Katuruka
567:Engaruka
492:See also
396:iron ore
385:charcoal
339:charcoal
278:Tanzania
264:complex
239:Cultural
150:Cultures
76:Tanzania
54:Location
1124:1746308
1104:Science
930:Tumbatu
902:Pangani
753:Kivinje
646:Kalenga
562:Laetoli
463:subsoil
406:Tuyères
400:tuyères
140:Periods
135:History
1283:
1258:
1228:529465
1226:
1182:
1130:
1122:
1082:21 Jul
1009:Mduuni
989:Chwaka
618:Kondoa
582:Peninj
82:Region
73:
1224:JSTOR
1180:JSTOR
1120:JSTOR
1064:Notes
994:Tumbe
907:Vugha
707:Ujiji
1281:ISBN
1256:ISBN
1128:PMID
1084:2022
381:slag
343:slag
333:The
260:are
236:Type
154:Haya
127:Type
1216:doi
1172:doi
1112:doi
1108:201
256:or
210:Yes
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