Marcia Selsor on wed 26 sep 07
Jon,
That is very good information. I have used playbox sand without
incident. But in a new place, I could see how not knowing what is in
the sand could be a problem. I suggested playbox sand in response to
Lisa's original post. Your comment regarding the pulverized seashells
reminded me of the experiences in Spain and Italy where in Spain the
pieces disolved after the bisque firing and in Italy where the clay
needs to be soaked to avoid disolving after the bisque firing. Do you
think the pulverized sea shells would be the cause? Is there enough
lime from the calcium of the shells to cause this?
What is your opinion? It is a phenomenon that intriques me.
Marcia Selsor
http://marciaselsor.com
On Sep 26, 2007, at 7:29 AM, Jon Pacini wrote:
> Greetings All---Hi Lisa
>
> There are a number of sands commonly available at your local hardware
> store, lumber yard and garden nursery. which one you use depends
> on the
> effect you want.
>
> Here's how you can get a handle on identifying them if the bags don't
> specify the composition.
>
> Silica sand is usually the cleanest most consistent--- white to
> pinkish
> in color, depending on the iron content.
>
> Feldspathic sand is gray and usually speckled with black--commonly
> used
> in mortars/cement mixes.
>
> Decomposed granite is dominantly tan with lots of variegation---
> usually
> available in a number of grades/colors for landscaping.
>
> Beach/play box sand varies a lot in color and composition---can have
> pulverized sea shell in it, that if coarsely ground, may or may not
> cause you grief in the form of pop offs.
>
> Best regards
> Jon Pacini
> Clay Manager
> Laguna Clay Co
Jon Pacini on wed 26 sep 07
Greetings All ---Hi Marcia----
You're right --beach/playbox sand can be used---depends on the composition.
An over abundance of Calcium in a bisque fired clay can inhibit it's
integrity. Even though it has been bisque fired and gone through the ceramic
change, when wetted it will break down. It will not become plastic again
because it has gone through the ceramic change, but it will break right down
in the presence of moisture.
A few years back I helped some guys who were experimenting adding cement to
their garden ware. They thought this would somehow add to it's strength. But
in effect it did the opposite and the ware even flaked apart when it sat
around in normal humidity. Nothing like opening up a kiln and watching the
pots turn back to dust before your eyes.
Cement of course is Calcined Limestone with some silica alumina and
magnesium present, but primarily Calcium from the Limestone. Seashells, also
being Calcium, will give you pretty much the same effect if they are finely
ground and in sufficient quantity. If they are in granular form they will
expand when wetted and cause pop offs if the ware does not have sufficient
strength to withstand the pressure.
Not sure how soaking the bisque ware in water would strengthen it, unless
there was so much lime present it was like making a pot entirely from
cement. Not sure what the mechanism at work there is.
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co
Marcia wrote----
Jon,
That is very good information. I have used playbox sand without incident.
But in a new place, I could see how not knowing what is in the sand could be
a problem. I suggested playbox sand in response to Lisa's original post.
Your comment regarding the pulverized seashells reminded me of the
experiences in Spain and Italy where in Spain the pieces disolved after the
bisque firing and in Italy where the clay needs to be soaked to avoid
disolving after the bisque firing. Do you think the pulverized sea shells
would be the cause? Is there enough lime from the calcium of the shells to
cause this?
What is your opinion? It is a phenomenon that intriques me.
Marcia Selsor
http://marciaselsor.com
On Sep 26, 2007, at 7:29 AM, Jon Pacini wrote:
Greetings All---Hi Lisa
There are a number of sands commonly available at your local hardware
store, lumber yard and garden nursery. which one you use depends on the
effect you want.
Here's how you can get a handle on identifying them if the bags don't
specify the composition.
Silica sand is usually the cleanest most consistent--- white to pinkish
in color, depending on the iron content.
Feldspathic sand is gray and usually speckled with black--commonly used
in mortars/cement mixes.
Decomposed granite is dominantly tan with lots of variegation---usually
available in a number of grades/colors for landscaping.
Beach/play box sand varies a lot in color and composition---can have
pulverized sea shell in it, that if coarsely ground, may or may not
cause you grief in the form of pop offs.
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co
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