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Re: applying images to ceramicsWARNING



Sil Horwitz wrote:

> At 2001/04/06 08:56 PM -0600, Herb Maxey wrote:
>
>> >>I have felt nervous about encouraging
>> >>a firing of dichromate but I suppose it is no worse that many
>> other common
>> >>glaze ingredients`
>>
>> Proceed at your peril. It is a dangerous material - ESPECIALLY when
>> it is heated. This chemical is not to be taken lightly. Ammonium
>> Dichromate is a known Carcinogen, it is toxic by inhalation and/or
>> ingestion and serious lung damage can result from breathing the
>> dust. It can cause liver and kidney damage as well as cause external
>> ulcers.
>
>
> Before you  go on  with your talk of doom and destruction, tell me:
> how much dichromate is left in the image after exposure and washing,
> before firing? I haven't made any studies, but I would surmise there
> isn't enough to register with ordinary qualitative analysis studies.
> I'll repeat: there should be no dichromate remaining after exposure
> and washing, no measurable amount that could do any harm. The
> dichromate is merely a catalyst to reform the structure of the colloid
> so that it becomes insoluble when exposed - it does not become a part
> of the colloid (gum or gelatin) molecules.

Whilst totally agreeing with thrust of  Sil augument .There is one part
of the above e-mail that needs some correction .

>>> The dichromate is merely a catalyst to reform the structure of the
colloid so that it becomes insoluble when exposed - it does not become a
part of the colloid (gum or gelatine) molecules.<<

In fact there could be is small chromium residue present after
processing. This residue can be observed if a piece of dichromated
colloid is exposed without any pigment being present.It manifests itself
as a brown orange stain and can be cleared in a number of ways the most
common is to use  a 5% bath of pot/sod/ metabisulfite or a long wash in
tap water  with the water slowly running12hrs to 24hrs.  After this
treatment the exposed portion will take on a blue/green grey look .I
have shown this to a chemist of my acquaintance who reckons it could be
a metallic chromium deposit.So there could be chrome present, but this a
big, but. And I seriously dought,  that this small amount of chemical
could pose any health hazard

Pete