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Linseed Oil Paints
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Updated Oct. 17th, 2017. Sample of Oxygen Deprived Oil, burnt plate oil without the flames...A new paint making strategy is developing based on the use of linseed oil almost exclusively.......
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The problem with linseed oil paints is their tendency to yellow. I've tried to bypass the yellowing issue by using other oils such as safflower, sunflower and soybean. These oils make weaker paint films but they do yellow less. As a compromise I was carefully blending some linseed oil into the weaker oils at a ratio of approximately 10-25% linseed to other oils. This works wonderfully and I could carry on with this strategy of blending oils if I wanted.
I like to keep things simple. It may not look that way by all the different directions I take, but in the long run I eventually find one path that is the most sensible. The linseed oil path is the one for me to take but it is not going to be easy.
How to deal with its inherent tendency to become yellow? Of all the linseed oil test samples I've created (1 or 2 hundred) only a few have not yellowed. All methods of hand-refining raw cold-pressed linseed oil have yellowed badly but samples of Graphics Chemical burnt plate oil are the least yellowing. It remains its initial colour of light amber forever it seems, never darkening even in the absence of all light. I'm sure there are other companies making similar types of oils, I have not tried them. What have they done to the oil to create this quality?
The answer seems to be that the oil has been modified by high heat in the absence of air to modify its fatty acids in such a way that the film becomes non-yellowing while maintaining its strength. No, they don't set boiling oil on fire anymore but it was a good way of depriving the hot oil of oxygen.
This is part of the linseed oil path for me, creating my own oxygen deprived heated oil.
The first problem is getting some good linseed oil at a reasonable price. Cold pressed is best. So far the best linseed oil I've used is my own, pressed at home straight from the seeds. The cost works out to about $11 a litre for raw oil. It refines very easily with no messy break which is probably due to the nature of straight pressing. The seeds are squashed flat, not mashed up like expellers do. My press uses a 20 ton hydraulic jack and I can press about a litre a day when necessary. It's not easy getting the oil out of the seeds. I would think a 20 ton jack is the bare minimum.
Linseed Oil Press
-20 ton multi-position hydraulic jack
-3 1/2" schedule 40 aluminum tube, removable for refilling
-3" pistons, one in each end of the tube
-2 short sections of I-beam, top & bottom of frame
-4 sections of 2"X2" angle iron
- misc. oak blocking and sliding plywood holders
-grade 5 bolts, 1/2" shank
Total materials cost= $200
The press is designed to be horizontal in order to make catching the dripping oil easier. This is also a more convenient position to apply leverage to the jack handle. This setup requires a multi-position jack although the fluid pickup tube inside a standard upright jack can be moved externally.
The seed cage, an aluminum tube, has tiny holes drilled in a loose pattern around the central area only. This is where the seeds will become compacted, in between 2 steel pistons consisting of 3" steel rod. In one end the piston is fixed so that only the jack end has a movable piston. The fixed end is pressed up against some oak blocking inside the I-beam end frame.
The seed cage can be removed for cleaning and refilling by sliding the plywood holders towards each end. These holders also keep the seed cage straight.
The hardest task in building the press was drilling the 1/2" holes. I only have electric hand drills, no drill press. Linseed oil makes a fantastic cutting fluid for drilling into the steel:) Be prepared to sharpen your bit often, this is a lot of steel to bore out. Eat more protein!
If you need help in designing an oilseed press or wish to have one custom built please feel free to send me an email. This is my 2nd press and I understand the principles involved.
This is an overhead view of the press showing the I-beam sections that make up the ends of the frame structure. Oak shimming between I-beam and angle irons was used to increase the space in order to fit the jack. It is compact and easily stored upright when not in use.
Oxygen Deprived Oil.
The goal of this endeavour is to heat refined linseed oil at 270-300 C. in the absence of air to create a heat bodied oil similar to burnt plate oil or stand oils. These types of oils don't yellow due to the changes in the fatty acids.
It is more difficult than expected. The first difficulty is creating a closed heating environment where air is prevented from oxidizing the oil as it heats. For this problem I have used an immersion lid which is simply a stainless steel bowl floating on the oil.
The immersion lid (a stainless steel bowl) has been dented in on one side to allow the thermometer access into the hot oil. It floats on the oil. This is a simple way to deprive the oil of oxygen although a tighter fit would be better. A deep tall pot helps. The oil's fumes will keep out most of the fresh air.
A piece of steel perforated sheet metal is used under the pot to buffer the heating element.
I would recommend this be done outdoors. It can be a fire hazard if overheated or knocked over while hot and the fumes are horrible as well as flammable when super-hot so a light breeze is good. Too much breeze will affect the heating. It is not easy to reach 300 C. Don't go higher as linseed oil has a flash point aroung 335 C. This means it must be closely montored as the oil will not lock in at a specific temperature. It wanders around.
I keep a bucket of sand nearby to extinguish a disaster if the need arises.
This is a confectionary thermometer. It has gone around the dial once and is now approaching 270 C. When it reaches the 100 mark it will actually be 300 C. My hot plate needs to be at max. to get there.
The oil was washed first, then dried at 150 C for 2 hours. It was heated at 270-300 C for 8 hrs. I was checking the oil by doing a string test. It's colour became dark but with a tighter immersion lid and perhaps less heating it could be lighter next time.
The sample is one month old. It dried in 2 days thin, 3+ days in the thick portion. It's a good drier with no stickiness. The sheen is glossy. This oil causes paints to melt and flow like enamel which is exactly what I expected. It is similar to a #2 or #3 burnt plate oil. More details soon...and much later (about 6 months) will be the yellowing test results.
Coming soon...epoxidized linseed oil or EPO. Another way to make linseed oil non-yellowing by chemically modifying the carbon-carbon double bonds of its unsaturated fats. Very exciting!
Also coming soon...The research into strontium as a safe drier is ongoing but so far it seems to be most effective as an acetate. I will post a formula to make strontium acetate soon. It seems to work best in the heated oils and seems to work very well in the epoxidizing process.