What was added to this glass to make it blue?

ink
lead
cobalt
magnesium
Powdered cobalt glass, called smalt, has been historically important as a pigment in painting and pottery. It is colored to a deep powder blue hue using cobalt ions derived from cobalt oxide. Cobalt aluminate can be used in a similar way, and is now more common, often known as "cobalt blue".
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ink
lead
cobalt
magnesium
answers
flagFinland
3%
0%
93%
3%
62
flagSwitzerland
5%
1%
92%
0%
70
flagItaly
4%
2%
88%
5%
94
flagthe United Arab Emirates
2%
2%
88%
5%
70
flagthe Netherlands
7%
2%
83%
5%
189
flagthe United Kingdom
10%
3%
79%
6%
908
flagGermany
11%
3%
79%
6%
392
flagSpain
9%
1%
79%
9%
54
flagFrance
13%
4%
78%
4%
69
flagCanada
9%
9%
77%
4%
74
flagPoland
15%
4%
74%
5%
30104
flagthe United States
9%
3%
72%
13%
1060
flagSweden
22%
5%
71%
1%
59
flagNorway
14%
3%
69%
11%
62
flagRepublic of Ireland
17%
5%
65%
11%
104
flagAustralia
18%
2%
65%
12%
70
flagUnknown
27%
4%
60%
6%
1368
flagIndia
21%
8%
56%
11%
509
flagthe Philippines
18%
4%
54%
21%
61
flagPakistan
33%
9%
35%
18%
54