[Ansteorra] cool home made stuff site

[David Hughes]

That's not a double boiler, it's a simple method of excluding air from
a melting pot.  Presumably used in this case to minimize oxidation
(typically darkening) of the heated resin, possibly to minimize fire
hazards.

A double boiler is a pot within a pot, with some heat transfer fluid
between them.  It prevents any hot spots on the inner pot, as it will
be no hotter than the fluid, and a maximum temperature can be set at
the boiling point of the fluid.

David Gallowglass

Christie Ward wrote:
>
> Erasmus asked:
> >does anyone know if double boilers are period ?
>
> Sure! Theophilus (ca. 1100) mentions one in a recipe for varnish:
>
> Set up four stones which can withstand fire without spalling, and place a
> raw pot upon them.  In the pot put some of the aforementioned resin, fornis,
> which is called glassa in Roman.  Over the mouth of this pot place a smaller
> one with a little hole in the bottom.  Smear some paste around it so that no
> air can escape between the two pots.  Then build a fire carefully beneath it
> until the resin melts.  You should also have a thin iron rod fitted into a
> handle, with which you can stir the resin and feel when it becomes
> completely liquid.  You should also have a third pot on the fire close by,
> with hot linseed oil in it.  When the resin is thoroughly liquid so that,
> when you take out the iron rod, a sort of thread is trailed behind it, pour
> the hot oil into it, stir with the rod, and cook them together without
> letting them boil.  Occasionally take out the rod and smear a little on a
> piece of wood or stone to test its consistency.  Take care that there are
> two parts of oil and a third part of resin by weight.  When you have cooked
> it carefully to your satisfaction, take it off the fire, uncover it, and let
> it cool.
>
> ::GUNNVOR::
>
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