last night I sanded a small boat in my basement. this morning I rememberd
I had left the linseed oil in my unheated workshop. it was too cold to
work with. I was going to heat it in a pan of water on the stove when I
caught sight of the microwave oven sitting on the kitchen counter. since
the linseed oil was in a plastic bottle I removed the top to keep the
bottle from exploding and put it in the microwave for half a minute at
meduim power. It turned the oil nice and runny. I put it back in the
microwave for another half minute on meduim heat and it came out runny and
warm like the white stuff in baby bottles. Mixed half-and-half with
universal solvent (paint thinner) in the usual manner the oil brushed on
like a dream.

(caution: It the oil were in a metal container it would have to be put in a
glass or plastic container before going in the microwave.)

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William R Watt National Capital FreeNet Ottawa's free community network
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I guess with a small amount there is no danger but I always worried
about the oil catching fire in the microwave. How do you know how much
to heat it without it reaching its flashpoint? I remember reading about
how linseed oil will spontaneously combust if on rags thrown in a trash
can. I always heated the oil in a double boiler type set up but I
wouldn't hesitate to use the microwave if I knew how to judge how long
to leave it in.

William R. Watt wrote:
last night I sanded a small boat in my basement. this morning I rememberd
I had left the linseed oil in my unheated workshop. it was too cold to
work with. I was going to heat it in a pan of water on the stove when I
caught sight of the microwave oven sitting on the kitchen counter. since
the linseed oil was in a plastic bottle I removed the top to keep the
bottle from exploding and put it in the microwave for half a minute at
meduim power. It turned the oil nice and runny. I put it back in the
microwave for another half minute on meduim heat and it came out runny and
warm like the white stuff in baby bottles. Mixed half-and-half with
universal solvent (paint thinner) in the usual manner the oil brushed on
like a dream.

(caution: It the oil were in a metal container it would have to be put in a
glass or plastic container before going in the microwave.)

--
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William R Watt National Capital FreeNet Ottawa's free community network
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steveJ ) writes:

.. I
wouldn't hesitate to use the microwave if I knew how to judge how long
to leave it in.

that's why I only put it in for 30 seconds at medium heat each time.
you could, I suppose, put it in and press the "beverge" button but I never
use that. when I heat a mug of water for tea I put it in for 2-and-a-half
minutes on high, so there is no danger at those temperatures.

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William R Watt National Capital FreeNet Ottawa's free community network
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It's a good idea and I have done similar things like melting
wax and even warming epoxy. But doesn't linseed oil have a really low
flashpoint temp. Something like 120 degrees or thereabouts?
William R. Watt wrote:
steveJ ) writes:


.. I
wouldn't hesitate to use the microwave if I knew how to judge how long
to leave it in.


that's why I only put it in for 30 seconds at medium heat each time.
you could, I suppose, put it in and press the "beverge" button but I never
use that. when I heat a mug of water for tea I put it in for 2-and-a-half
minutes on high, so there is no danger at those temperatures.

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steveJ ) writes:

...doesn't linseed oil have a really low
flashpoint temp. Something like 120 degrees or thereabouts?

Had to look it up ...

"flash point: the lowest temperature at which the vapours of
petroleum or other combustable liquids will give a flash or slight
explosion on exposure to a flame"

there's no flame in a microwve oven. I don't know if the magnetron
gets hot enough to ignite vapours. I didn't smell any vapour. It
smells like paint drying because linseed is the oil in paint.
Pretty unmistakable. The oven itself didn't get warm, just the
oil, so I doubt the magnetron was hot.

I'm sure at the low temerature and short duration I was using the oven
there would not be a "slight explosion". In fact there wasn't. But if I
try it again and smell any vapour I'll be sure to press the button that
opens the door and shuts off the magnetron. Thanks for the caution.

Is is safer heating linseed oil on a stove top in the presence of a hot
stove element?


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William R. Watt wrote:

(caution: It the oil were in a metal container it would have to be put in a
glass or plastic container before going in the microwave.)

Why?

Rick

Rick ) writes:
William R. Watt wrote:

(caution: It the oil were in a metal container it would have to be put in a
glass or plastic container before going in the microwave.)

Why?

because you can't put metal containers in a microwave oven. they reflect
the microwaves instead of letting them pass through into the stuff inside.
I've never tried putting a metal container in a microwave but its supposed
to be noisy and ruin the microwave oven. There is one exception which is a
metal container with a sepcial coating for microwaves. I have an aluminum
pie plate coated for microwave use which I put under other containers
sometimes to catch drips of condensation.

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William R Watt National Capital FreeNet Ottawa's free community network
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I've been cautioned to use a double boiler setup on the stove to avoid
fire. The water beneath the pot containing the oil does not contact
flame directly so it is safer.

William R. Watt wrote:

Is is safer heating linseed oil on a stove top in the presence of a hot
stove element?


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William R Watt National Capital FreeNet Ottawa's free community network
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Actually the flashpoint is 145 deg F.
Here is the MSDS for what it's worth.
http://www.generalpaint.com/msds/32-002.html

William R. Watt wrote:
steveJ ) writes:


...doesn't linseed oil have a really low
flashpoint temp. Something like 120 degrees or thereabouts?


Had to look it up ...

"flash point: the lowest temperature at which the vapours of
petroleum or other combustable liquids will give a flash or slight
explosion on exposure to a flame"

there's no flame in a microwve oven. I don't know if the magnetron
gets hot enough to ignite vapours. I didn't smell any vapour. It
smells like paint drying because linseed is the oil in paint.
Pretty unmistakable. The oven itself didn't get warm, just the
oil, so I doubt the magnetron was hot.

I'm sure at the low temerature and short duration I was using the oven
there would not be a "slight explosion". In fact there wasn't. But if I
try it again and smell any vapour I'll be sure to press the button that
opens the door and shuts off the magnetron. Thanks for the caution.

Is is safer heating linseed oil on a stove top in the presence of a hot
stove element?


--
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William R Watt National Capital FreeNet Ottawa's free community network
homepage: www.ncf.ca/~ag384/top.htm
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steveJ wrote:

I remember reading about
how linseed oil will spontaneously combust if on rags thrown in a trash
can.

This will only occur if the rags are wadded up. The oil in the rags
oxidizes, producing heat which can build up and eventually cause a fire.
If you leave a rag open, it cannot happen as normal airflow will prevent
heat buildup.