DOI Seite / Zitierlink:
https://doi.org/10.11588/diglit.36284#0051
43
The examination of the blue enamel furnished inter-
esting particulars. A sufficient mass of this was placed
before me to enable me to make not only a qualitative
analysis, but also a sufficiently exact quantitative analysis also.
Under the microscope, the enamel showed clearly grains
of blue colour imbedded in a colourless vitreous mass.
The analysis revealed that the enamel was absolutely
free from cobalt, copper, and lead; also that there was
no boracic acid in it. On the contrary, there were all the
elements of the glass-mass of the fragment : potter's earth,
iron, manganese, lime, magnesia, and alkalies.
Thus there were absent here the oxides of cobalt and
of copper, once regarded as the only blue-colouring
principles for glass and enamel. Even the most subtle
re-agents failed to discover any trace of them.
The impression forced itself upon my mind that in
some way (for which there is nothing analogous in the
technique of glass), the lapis lazuli—a semi-precious
stone—had been used for the colouring of the enamels.
A splinter of the blue enamel brought into a smelting
borax-pearl, is dissolved in it on the spot in a brownish
vapour. Precisely the same result attended a similar
treatment of a splinter of lapis lazuli.
There are analyses of lapis lazuli, made by several
investigators (Dammer, Anorganische Ohemie, 1893, Yol.
Ill, p. 194; Rammelsberg, Mineralchemie, 1875, p. 458).
They give the following list for the synthesis of that
mineral:—
Sulphur
Sulphuric acid
Potter's earth
Silicious earth
Peroxide of iron
Lime
Natron .
Chlor .
0-95
1-92
12-33
40-54
0-86
114
8-76
0
3- 961
5-98 7.
43-007.
45-70 7.
4- 20 7.
23-56 7.
11-45 7.
0-42 7.
Characteristic in the silicated mineral, are the holding
of sulphur (in the form of sulphuric acid), and the high
degree of potter's earth.
This must also be remarkable in the synthesis of the
blue enamel.
The quantitative analysis, performed with 0*1200
grains of substance, came out thus :—
Sulphuric acid — SOg . . 1*1 7.*
Potter's earth . . . 6*7 7.
Silicious earth . . . 56*67.
Peroxide of iron . . . 1*3 7.
Protoxide of Manganese . 1*9 7.
Lime.4-7 7.
Magnesia .... 3*7 7.
Balance of alkalies . . 24*07.
4
* The substance was disintegrated with bromic acid, and thereby all
sulphur maintained as sulphuric acid.
Thus we discover in the enamel, the elements of the
glass-mass—characteristically the magnesia and manganese
deposits—but a much greater holding of potter's earth and
also sulphuric acid.
From this we might conclude that the Arab glass-
artists manufactured the blue enamel by rubbing the lapis
lazuli with powdered glass—probably a smelted glass made
weakly fluid by the heightening of the quantity of alkalies
contained in it.
With the addition of lead, as usual, the fluid glass
would not here have become fluent, as lead glass will not
mingle with the sulphur-holding lapis lazuli and becomes
black. In agreement with this is the fact that the Arabic
blue enamel exhibits no real enamel-lustre, but a sort of
macaroni-looking surface, and is considerably harder than
the other lead-holding colour-enamels.
A direct attempt established these conclusions.
Lapis lazuli rubbed with powdered glass gave a blue
enamel smeltable on glass, to which only purity and depth
of colour were lacking; as I had no clear deep-coloured
lapis to make use of.
The colour-substance of the lapis lazuli is used to-day
in art manufacture to a great extent; this is the ultra-
marine blue of trade.
With this ultramarine blue, rubbed with a vitreous
mass (1 NagO, 1 KgO, 1 CaO, 6 SiOg) we succeeded in
producing an enamel like the Arab enamel in colour-tone
and in character.
I know of no statement in technical glass literature,
that with ultramarine or lapis lazuli, a blue enamel-colour
is producible or has ever been produced; nor do I know
of any analysis which has recorded the absence of the
two metals, cobalt and copper, in a blue enamel.
This cobalt-less lapis lazuli blue may for the present
be taken as the direct characteristic of old Arabic glass-
work, and must, as against imitations, take its place as
a chemical criterion.
DR. F. LlNKE,
P?%p e rhJ -Roy a ^ Pro/essor.
Vienna, 3rd, 1896.
Chemical Laboratory of the Imp.-Roy.
School of Art-Industry.
A confirmation of this discovery has since taken place,
through the examination of the Arabic mosque-lamp of the
fifteenth century (Inventar, no. 9949) in the Austrian
Museum for Art and Industry.
The blue enamel of this lamp was recognised as
without cobalt, and made with lapis lazuli, while the blue
enamel, externally very similar to it, of an imitation-vase
by Brocard of Paris (Inventar, no. 7552) owes its colour to
cobalt oxide.
Vienna, IsarcA 14^A, 1898.
The examination of the blue enamel furnished inter-
esting particulars. A sufficient mass of this was placed
before me to enable me to make not only a qualitative
analysis, but also a sufficiently exact quantitative analysis also.
Under the microscope, the enamel showed clearly grains
of blue colour imbedded in a colourless vitreous mass.
The analysis revealed that the enamel was absolutely
free from cobalt, copper, and lead; also that there was
no boracic acid in it. On the contrary, there were all the
elements of the glass-mass of the fragment : potter's earth,
iron, manganese, lime, magnesia, and alkalies.
Thus there were absent here the oxides of cobalt and
of copper, once regarded as the only blue-colouring
principles for glass and enamel. Even the most subtle
re-agents failed to discover any trace of them.
The impression forced itself upon my mind that in
some way (for which there is nothing analogous in the
technique of glass), the lapis lazuli—a semi-precious
stone—had been used for the colouring of the enamels.
A splinter of the blue enamel brought into a smelting
borax-pearl, is dissolved in it on the spot in a brownish
vapour. Precisely the same result attended a similar
treatment of a splinter of lapis lazuli.
There are analyses of lapis lazuli, made by several
investigators (Dammer, Anorganische Ohemie, 1893, Yol.
Ill, p. 194; Rammelsberg, Mineralchemie, 1875, p. 458).
They give the following list for the synthesis of that
mineral:—
Sulphur
Sulphuric acid
Potter's earth
Silicious earth
Peroxide of iron
Lime
Natron .
Chlor .
0-95
1-92
12-33
40-54
0-86
114
8-76
0
3- 961
5-98 7.
43-007.
45-70 7.
4- 20 7.
23-56 7.
11-45 7.
0-42 7.
Characteristic in the silicated mineral, are the holding
of sulphur (in the form of sulphuric acid), and the high
degree of potter's earth.
This must also be remarkable in the synthesis of the
blue enamel.
The quantitative analysis, performed with 0*1200
grains of substance, came out thus :—
Sulphuric acid — SOg . . 1*1 7.*
Potter's earth . . . 6*7 7.
Silicious earth . . . 56*67.
Peroxide of iron . . . 1*3 7.
Protoxide of Manganese . 1*9 7.
Lime.4-7 7.
Magnesia .... 3*7 7.
Balance of alkalies . . 24*07.
4
* The substance was disintegrated with bromic acid, and thereby all
sulphur maintained as sulphuric acid.
Thus we discover in the enamel, the elements of the
glass-mass—characteristically the magnesia and manganese
deposits—but a much greater holding of potter's earth and
also sulphuric acid.
From this we might conclude that the Arab glass-
artists manufactured the blue enamel by rubbing the lapis
lazuli with powdered glass—probably a smelted glass made
weakly fluid by the heightening of the quantity of alkalies
contained in it.
With the addition of lead, as usual, the fluid glass
would not here have become fluent, as lead glass will not
mingle with the sulphur-holding lapis lazuli and becomes
black. In agreement with this is the fact that the Arabic
blue enamel exhibits no real enamel-lustre, but a sort of
macaroni-looking surface, and is considerably harder than
the other lead-holding colour-enamels.
A direct attempt established these conclusions.
Lapis lazuli rubbed with powdered glass gave a blue
enamel smeltable on glass, to which only purity and depth
of colour were lacking; as I had no clear deep-coloured
lapis to make use of.
The colour-substance of the lapis lazuli is used to-day
in art manufacture to a great extent; this is the ultra-
marine blue of trade.
With this ultramarine blue, rubbed with a vitreous
mass (1 NagO, 1 KgO, 1 CaO, 6 SiOg) we succeeded in
producing an enamel like the Arab enamel in colour-tone
and in character.
I know of no statement in technical glass literature,
that with ultramarine or lapis lazuli, a blue enamel-colour
is producible or has ever been produced; nor do I know
of any analysis which has recorded the absence of the
two metals, cobalt and copper, in a blue enamel.
This cobalt-less lapis lazuli blue may for the present
be taken as the direct characteristic of old Arabic glass-
work, and must, as against imitations, take its place as
a chemical criterion.
DR. F. LlNKE,
P?%p e rhJ -Roy a ^ Pro/essor.
Vienna, 3rd, 1896.
Chemical Laboratory of the Imp.-Roy.
School of Art-Industry.
A confirmation of this discovery has since taken place,
through the examination of the Arabic mosque-lamp of the
fifteenth century (Inventar, no. 9949) in the Austrian
Museum for Art and Industry.
The blue enamel of this lamp was recognised as
without cobalt, and made with lapis lazuli, while the blue
enamel, externally very similar to it, of an imitation-vase
by Brocard of Paris (Inventar, no. 7552) owes its colour to
cobalt oxide.
Vienna, IsarcA 14^A, 1898.