Pottery In Australia Vol 36 No 2 Winter 1997

GREAT
GLAZES
Colouring Translucent Bone China
GABRIELLE FLEET, currently studying for a Masters at Monash University, Caufield.
I
devised a means of colouring a highly translucent hone
china, without noticeably affecting the translucency.
This was achieved using water soluble metal salts.
Conventional methods of colouring ceramics render it
opaque which is inappropriate for my work. For my
application the colouranlS are used for the transmittance of
light. This reveals beautiful and almost Auoresent colours
when placed before a halogen lamp. The sole use of
nitrates instead of sulphates and chlorides is intentiona l.
Nitrates are the most soluble of the metal salts and are
ge nerally the most stable and least volati le during
decomposition to the oxide. during the firing priocess. The
gases evolved during the decomposition of the nitrates are
the least toxic and corrosive of the soluble metal sailS.
These tests were executed without unnecessary use of
protective masks and fume hoods but with only latex
gloves to protect my skin from absorbing the water
soluble compounds. There are no fumes asociated with
these water sol uble compounds, and the only vapour
evaporating from the metal salt solution is wate r. The
only possible risk is through ingestion or absorbtion of a
considerable quantity through the skin.
Water soluble coloura nlS - painted onto bisqued test tiles.
The natu ral bone ash content is suplemented with
Fe (N03)3 Very translucent, golden brown, yellow
Co(N03)2 Translucent purple
Cu( 03)2 Very translucent turquoise
cre 03)3 Translucent, grass green
TRANSLUCENT
BONE ASH BODY
Ingredient %
atural bone ash ?' - )
Synthetic hone as 25
Nepheline syen ire 27
Ecka lite I 30
Macaloid 25
Fire to 126O"C
symhetic bone ;Ish because of the impractical and time
consuming grinding and sieving of the natural bone ash.
This formulation is seived 5 times to remove any lumps
and th en ball mill ed for 8-10 hours. The hydrated
macaloid is added after th e ball milling to avoid
destroying the plastic qualities of the macaloid. This was
the most practical of the recipes I tested as it maintained
high translucency and retained effective plasticity. 00
36/2 WINTER 1997 + POTTERY IN AUSTRAUA 57