Analyses of slag

It is neccessary to achieve proper quality of slag at the smelting process. Ancient smelters in Bohinj reached that by adding silicon sand to the ore charge.

The lowest melting point (1150 °C) is reached  by fayalitic slag which has the proportion of the main components of slag 2,4  (%FeO / %SiO2 = 2,4).

Norwegen arheometallurgist Arne Espelund  proves that their slag reaches fayalitic factor from 2,2 to 2,4 . 

Different viscousity of slag is seen on photos. The upper shows smelting in 2001 with adding 20 % of silicon. The lower is from 2016 where the slag is hardly running. Both smelting was peformed at th same temperature and with the same ore. In methallurgical theory the slag sistems are known which explain the same.

The problem appear later at smithing. A part of bloom from 2016 was smithed but the smithing was bad. The slag was sticking to iron. At heating in the hearth the slag was not liquid..  

 

Now we have to compare slag analyses from smelting in 2001 to the ancient slags. The table shows average analysis fom Aj. gradec and Dunaj at Jereka and those from smelting in 2001.

SLAG Fe Fe2O3 FeO SiO2 Al2O3 CaO MgO MnO
Ajd.gradec
51,8
8,72
59,69
21,68
5,51
3,97
1,06
0,34
Dunaj at Jereka
48,9
10,72
53,26
24,25
3,81
2,89
1,14
0,96
smelting 2001
49,0
5,51
57,94
24,80
6,99
3,06
0,81
0,07

 

The table shows equality of ore oxides and fayalitic proportion about 2,4.

We can conclude that ancient smelters used the same ore and the same addition of silicon as we did.

žlindra

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Slag from smelting experiment in 2001

žlindra

 

 

 

 

 

 

 

 

 

 

 

 

Slag from smelting experiment in 2016

Very interesting are also chemical analyses of slag from different locations in Bohinj that were made by some researchers (Morlot, Rjazancev and probable Šmid).

LOCATION
 author of analyse Fe(tot) FeO Fe2O3 SiO2 Al2O3 CaO MgO Mn2O3 P2O3
Ajd.gradec Morlot
53,30
69,10
20,31
6,40
3,00
Ajd.gradec Rjazancev
53,17
64,77
4,04
22,02
3,45
3,29
0,90
0,45
0,46
Ajd.gradec Rjazancev
49,82
59,10
5,55
24,88
4,18
4,05
1,13
0,36
0,50
Ajd.gradec Rjazancev
48,02
45,78
16,59
19,52
8,00
5,53
1,17
0,21
0,64
Ajd.gradec average
51,08
59,69
8,72
21,68
5,51
3,97
1,06
0,34
0,53
   
Dunaj at Jereka  
55,47
59,90
12,74
19,39
1,28
3,10
1,15
1,14
0,34
Dunaj at Jereka  
42,32
46,32
8,69
28,66
6,33
2,68
1,12
0,77
0,32
Dunaj at Jereka average
48,90
53,26
10,72
24,25
3,81
2,89
1,14
0,96
0,22
   
Studor Rjazancev
68,98
74,17
16,20
3,00
2,69
2,24
1,02
0,40
0,36
Studor Rjazancev
58,80
52,66
25,55
5,35
2,10
9,63
1,77
0,18
0,41
Studor Rjazancev
44,59
53,53
4,26
26,58
6,65
4,14
0,96
2,18
0,73
Studor Rjazancev
46,58
56,61
4,07
29,06
5,43
1,62
0,64
1,21
0,41
   
Mošenac  
69,84
77,50
13,72
2,03
2,31
1,46
0,64
0,57
0,38
Mošenac Rjazancev
70,47
82,30
9,29
2,34
1,80
1,00
0,40
1,71
0,34
Mošenac  
69,47
77,54
13,15
2,58
2,08
2,13
0,64
0,75
0,40
Mošenac average
70,00
79,10
12,05
2,31
2,06
1,53
0,56
1,31
0,37

The table shows different locations from different time of operating. Mošenac is proclaimed to be alive in the early Middle Age. Studor is probably from Iron and Middle Age. If we are focused on FeO and SiO2 and calculate fayalitic factor we can conclude that smelters at Ajdovski gradec and Dunaj were masters of their work.

Location of Mošenac from early Middle Age proves bad smelting knowlege, without addition of silicon and high percentage of total iron in slag which means lower yield of iron. Many authors prove the same: abilities of ancient iron smelters were never reached.

 

Look also: