[Cob] Linseed and sunflower oil

[Amanda Peck]

there is a Chinese tree (Aleurites fordii, known as tung oil tree, tung 
tree, China oil tree, etc.) whose seeds yield a yellowish oil that is good 
for furniture finishing.  The ads claim that it is non-yellowing.

Here's a bit on tung oil from one company--woodworker's supply, scroll down 
a bit

http://woodworker.com/cgi-bin/search.exe?search=tung%20oil&go=388

A tung oil mixture was widely used with "Danish Modern" furniture, although 
one item in a search on "Danish oil" told me that it had been used by Danish 
craftspeople for centuries..  By the time tung oil gets called "Danish Oil" 
it may have driers, probably something to dilute it, maybe linseed oil, I've 
even heard of UV inhibitors added--but it may have been called "teak oil" by 
then.

The process of successive dilutions of tung or linseed oil with mineral 
spirits or turpentine apparently began with furniture, at least from what my 
quick searches indicated.


.............
Jane wrote (she knows what she's talking about, it's wonderful):

According to my teachers in wood carving and the like linseed oil has
special properties. It hardens as it dries which creates a (more or less)
watertight surface. Boiled linseed oil hardens faster, but raw linseed oil
also hardens after some time - how fast and how well depends on the
quality of the oil.

(One problem with buying boiled linseed oil is that it normally contains
rather toxic chemicals to ease the drying. It might be possible to buy
non-toxic boiled linseed oil, though.)

It is possible that cooking other kinds of oil will make them harden too,
but I have never heard of it. And for a floor you definitely need a
hardened surface. From what I have heard getting a good surface on a clay
floor is pretty tricky, and even if sunflower oil works for paint, it
doesn't follow that it works for floors.

It would be an interesting experiment, though.

It wonder what this "danish" tung oil you write about is (I'm danish). We
have something called "tonkin-laque" which is based on linseed oil, and
which is supposed to make a very resistant surface. If tung oil is the
same as tonkin-laque i would suppose that you could make a cob bathtub
with it, though you would probably have to re-laquer it at regular
intervals, and leave it to dry and hardenfor some time before using it
again.

And a warning: From what I have learned you risk spontaneous combustion
with ALL linseed oil, not only boiled. So never leave linseed oil soaked
paper or cloth around. The simplest thing is to burn it right away, or at
least leave it on the stove or fireplace, but if we are talking large
quantities this might not be so environmantal friendly. You can also put
it in water, but then you have to do something with it afterwards.

Jane