[Clayart] durable outdoor planters

[sumi]

Phyllis

Many potters will say you want a clay body with as little absorbency as 
possible. However, what I've been reading is that you want a clay body 
with the correct saturation coefficient. This is calculated by weighing 
a dry, fired test tile, then soaking it in water for 24 hours, then 
drying and weighing again. Then, boil them for 5 hours, dry them off, 
and weigh again.

Divide the soaked absorption rate by the boiled absorption rate to get 
the saturation coefficient.

SO:

(Soaked weight - dry weight) divided by dry weight = soaked absorption rate

(Boiled weight - dry weight) divided by dry weight = boiled absorption rate

Soaked absorption rate divided by boiled absorption rate = saturation 
coefficient.

If your clay absorbs 3% when soaked and 4% when boiled, your saturation 
coefficient is .75

Saturation coefficient should be less than .78

I've seen sources state it should be less than .78, some say "about .78"

Not sure which is correct.

Sumi
>   I have made several planters over the course of my pottery passion. Some
> of them hold up to the winter (occasional freezing temperatures), and some
> don't. I would love to be able to pinpoint what I am doing both right and
> wrong because I would like to make some larger sized planters. But of
> course I want them to be able to withstand the occasional freezing
> temperatures that we get in Virginia. Does anyone have any suggestions or
> tips for making these pots? I do both handbuilding and throwing but I will
> probably make these planters from extruded coils. As always, thank you in
> advance for your help.
> Phyllis Canupp
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