Follow on to red lead:

Minium, which has been known as "red lead", is an oxidation product of other
lead minerals. It forms in extreme oxidizing conditions of lead ore bodies
and its presence is very indicative of the degree of oxidation. Something of
interest to petrologists (rock scientists). It is probably more common than
is known as it exists as a slight reddish coating on many lead specimens,
often to the detriment of the aesthetic appeal of the underlying mineral.
However, some specimens are exceptional and boast a bright red color with a
high adamantine luster. The best specimens in the world come from Broken
Hill, New South Wales, Australia. Unfortunately, these specimens are the
result of a mine fire and mineral purists do not like their human influenced
origins.
Minium gets its name from the Minius River in Northwest Spain. The name,
minium has also been applied to cinnabar, a red mercury sulfide, but now it
is exclusively used world wide to refer to the red lead oxide. Minium is
more well known to the makers of pigments than it is to mineral collectors.
The artificially produced minium is used as a pigment in paints and dyes
although the health concerns of lead have greatly diminished this role.

Minium is a member of the Spinel Group of oxide minerals. The general
formula for the Spinel Group is AB2O4. Minium with its formula of Pb3O4, may
not look like it belongs. But the lead in minium is actually composed of two
different valence states (Pb +2) and (Pb +4). If its formula is rewritten
with the different valence states indicated then the formula appears as in
classic Spinel Group form as (Pb +4)(Pb +2)2O4. The two different valences
of lead occupy different locations in the spinel type structure. Minium's
structure is not exactly the same as spinel as spinel is an isometric
mineral and minium is a tetragonal mineral. The small size of the lead ions,
no doubt, cause a distortion in the spinel structure.


THE PHYSICAL CHARACTERISTICS OF MINIUM:
Color is red, scarlet to brick-red.
Luster is greasy to adamantine.
Transparency: Crystals are opaque.
Crystal System is tetragonal; bar 4 2 m
Crystal Habits include scaly aggregates and powdery coatings on other lead
minerals. Also massive and granular. Crystals are generally well striated.
Cleavage is perfect in several directions.
Fracture is uneven.
Hardness is 2.5 - 3.
Specific Gravity is 8.9 - 9.2 (Well above average for any mineral).
Streak is orange yellow.
Other Characteristics: Some specimens fluoresce an orange color under
ultraviolet light.
Associated Minerals include massicot, galena, wulfenite, pyromorphite,
mimetite, bindheimite, cerussite, lead, duftite and sphalerite.
Notable Occurrences include its name originator, the Minius River in
Northwest Spain as well as Inyo County, California; several localities in
Arizona; Leadville, Colorado and at the Jay Gould Mine, Idaho, USA; Broken
Hill, New South Wales, Australia; Altai Mountains, Russia; Eifel region of
Germany and at Lavrion, Greece.
Best Field Indicators are color, crystal habit, streak, density and
softness.

----- Original Message -----
From: "Stephen P. Austin" <[log in to unmask]>
To: <[log in to unmask]>; <[log in to unmask]>
Sent: Thursday, August 02, 2001 7:32 PM
Subject: Re: PA German Potteries


> Red lead is another name for the powder form of mercury. It was a deep
> maroon red.  Once available years ago in hardware stores.  Don't know what
> it was used for.  Heat it and it will 'melt' into the silver stuff you are
> familiar with.  Don't know what color it produced in a kiln - yellow
> (amarillo) I think.
>
> ----- Original Message -----
> From: "Mary Jane Shaw" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, August 02, 2001 9:17 PM
> Subject: PA German Potteries
>
>
> > I have excavated a late 18th century and possibly early 19th century
> > Pennsylvania German pottery site in southwestern Pennsylvania. Am
> > currently writing the site report. It was, unfortunately, a salvage
> > dig.    Represented on the site were basic utilitarian redware vessels,
> > glazed on the interior, a small amount of vessels with glazing on the
> > interior and exterior, a very small quantity of slip-decorated redware
> > and one experimental, decorative piece. No salt glazing is evidenced.
> >         I am seeking information on the types of glazes used, as well as
> their
> > sources. Lead would have been easily obtainable, but what really is red
> > lead? Could the potter have obtained white clay? Many pieces exhibit a
> > thin white coating, but no engraving or other applied decoration. I have
> > basic general knowledge of potting and glazing, and have consulted Edwin
> > Atlee Barber's book regarding Pennsylvania German potters, among others.
> > Additionally, I am seeking information about a hard-fired, thin, not
> > glazed, redware that I do not think was manufactured here. It may have
> > been of English origin. I have read where England did export basic
> > redware in this time period. It may have been made in eastern PA by an
> > English potter.
> >         I welcome all comments and input/direction.
> >
>