Earl Brunner on wed 10 nov 99
Our studio used to have a Plum glaze with Potassium Dichromate in it.
Having the Potassium Dichromate around really bothered me, so I
reformulated the recipe using calulation software. Initally, according
to the computer the recipe called for a substitution of 1.1 % Chrome
oxide. That made it too dark and a little muddy. As we have used up
the batch, I have added several gallons of base without any chrome until
we finally have a really nice plum color that matches the original very
Volcanic ash 54
Gerstley Borate 18.6
Tin oxide 6.7
Chrome Oxide (green) 1.1
I estimate the newer percentage at around .5% maybe a little less
I am just wondering if I am correct in assuming that the new plum is
safer than the old one.
Volcanic ash 51.6
Gerstley Borate 18.4
tin ox 6.6
Potasium Dichromate (really nasty stuff) 2
Edouard Bastarache on tue 16 nov 99
Potassium is not toxic.Any toxicity of the salts is due to the anion.
The following salts are known to be hazardous: arsenate, arsenite,
bichromate, chromate, cyanide, hydroxide, permaganate.
When heated to decomposition they emit toxic fumes of K2O.
Potassium bichromate: Human poison by ingestion. An experimental
poison by ingestion, intraperitoneal, intraveinous, and sub-cutaneous
routes. Human mutagenic data.
One synonym is Potassium dichromate(VI).
Dichromates belong to Group =234 of ACGIH=3DHexavalent chromium compounds,
which are compounds that may cause chrome ulcers, irritative dermatitis,
or nasal septal perforation.
Certain hexavalent chromium compounds have been demonstrated to be
carcinogenic on the basis of epidemiological investigations of workers
and experimental studies with animals..In general, these tend to be of low
solubility in water and, thus, are subdivided into two subgroups:
A-Water-soluble hexavalent chromium compounds
to which potassium dichromate belongs.
B-Water-insoluble hexavalent chromium compounds: such as lead chromate,
strontium chromate, etc.
Now if you have used green chromic oxide, here is the toxicity that applies:
Chromium for Potters:
Chromium can have a valence of 2, 3, and 6. Chromium compounds vary greatly
in their toxic and carcinogenic effects.For this reason ACGIH divides
chromium and its inorganic compounds in a number of groupings.
Group =233 is =AB Trivalent chromium compounds =BB
(Cr3+)(chromic compounds) :including chromic oxide (Cr2o3) which is green
chromic oxide, chromic sulfate, chromic chloride, chromic potassium sulfate,
Green chromic oxide is the one i use and i think it is the same for all of
potters=3B the nastiest being hexavalent chromium compounds of group =234, =
not think governement officials would let us use the latter.
So what applies is the toxicology of trivalent compounds.
Routes of Absorption : Chromic salts are minimally absorbed following
inhalation.Trivalent chromium salts are generally poorly absorbed through
intact skin, once the dermal barrier is broken, however, absorption may
occur. Trivalent chromium salts are absorbed following ingestion, but only
1-25=25 of the dose ingested is absorbed.
There is little evidence of significant toxicity from chromic salts,
probably because of poor penetration of skin and mucous membranes.Dermatitis
from chromic salts has been reported.
The lungs of some workers exposed to chromite dust have been shown to be the
pneumoconiotic changes consisting of slight thickening of interstitial
tissue and alveolar septa, with histological fibrosis and hyalinisation.
A refractory plant using chromite ore to make chromite brick had no excess
of lung cancer deaths over a 14-year period.
Inhalation of trivalent chromium salts can cause occupational asthma.
The IARC(International Agency for Research on Cancer, Lyon ,France) has
determined that there is inadequate evidence in humans and animals for the
carcinogenicity of metallic chromium and trivalent chromium compounds(III).
Trivalent compounds, do not appear to cause other effects associated with
the hexavalent chromium compounds, such as chrome ulcers (hands and
forearms), irritative dermatitis, nasal septal perforation, lung cancer,
You have certainly improved the situation.
See you later on =23pottery,
1-Chemical Hazards of the Workplace, Proctor =26 Hughes.
2-Dangerous Properties of Industrial Materials, Sax =26 Lewis.
3-Hazardous Materials Toxicology, Sullivan =26 Krieger.
De : Earl Brunner =3Cbruec=40anv.net=3E
=C0 : CLAYART=40LSV.UKY.EDU =3CCLAYART=40LSV.UKY.EDU=3E
Date : 15 novembre, 1999 11:38
Objet : Cone 6 Plum
=3EOur studio used to have a Plum glaze with Potassium Dichromate in it.
=3EHaving the Potassium Dichromate around really bothered me, so I
=3Ereformulated the recipe using calulation software. Initally, according
=3Eto the computer the recipe called for a substitution of 1.1 =25 Chrome
=3Eoxide. That made it too dark and a little muddy. As we have used up
=3Ethe batch, I have added several gallons of base without any chrome until
=3Ewe finally have a really nice plum color that matches the original very
=3EVolcanic ash 54
=3EGerstley Borate 18.6
=3ETin oxide 6.7
=3EChrome Oxide (green) 1.1
=3EI estimate the newer percentage at around .5=25 maybe a little less
=3EI am just wondering if I am correct in assuming that the new plum is
=3Esafer than the old one.
=3EVolcanic ash 51.6
=3EGerstley Borate 18.4
=3Etin ox 6.6
=3EPotasium Dichromate (really nasty stuff) 2