Sun Thickened Linseed Oil

Knowing how to make and use this oil medium is probably the greatest secret a painter can learn. It is truly remarkable stuff, and yet it can be made easily by artists with minimal cost and effort. Before I tell you how to make it, I have to extol its virtues, because if you understand and learn to appreciate its potential it will have a profound effect on your paintings. I cannot emphasise this enough. It will allow you to form a glaze to stretch out colour without it ever breaking or failing. It can mix with your paint to form such a delicate and fine layer that the colour reduces to a point where your eye can no longer be sure it’s actually there. Or to put it another way, imagine creating a shadow on the side of a face with burnt umber, which you want it to fade very softly at the edge where it meets normal light. Linseed oil mixed with colour will allow you to fade it in a wonderfully controlled way, without the colour smudging to nothing on the canvas or, as may be the case, onto the dried paint of the cheek below your shadow. It also speeds up the drying of all paint and mediums with which it is used.

What you will need:

  • 1 cooking pan, measuring 10 x 7 and about 4 inches deep (25.4cm x 17.8cm and 10.2cm deep)
  • 1 glass sheet, slightly bigger than the pan
  • 4 pieces of wood – matchsticks are ideal
  • _ Litre or _ pint Linseed oil


Take a litre or so of refined linseed oil and pour it in a metal tray. Enamel cooking ones are ideal. Pour enough oil in to create a depth of half an inch (12mm). You will need a glass sheet slightly bigger than the pan to cover it over. Place 4 small pieces of wood (discarded matches are ideal) to act as spacers so the glass sheet is slightly lifted off the cooking pan. This allows the passage of air and keeps most airborne rubbish out, although any errant flies will have to be removed by the butler! Leave it in a window in direct sun light and stir or whisk it every other day for a minute or so, just as you would eggs. This will aerate it, and you will find after 10-15 days it is becoming thicker and more gloopy in texture. The longer you continue the process the thicker the texture will become. The density of the texture is a matter of personal preference. The thicker the viscosity the greater the handling power and it is something you will have to explore until you decide what is best for you.

28 Responses to “Sun Thickened Linseed Oil”

December 29, 2016 at 12:43 am, Sarmed said:

Great tip! Would love to try it but where do I get the daily dose of sun during a Scottish winter, or summer for that matter 🙂 ?


December 26, 2017 at 6:53 pm, Alejandro said:

> In that case you may bubble your oil for about two weeks with air from an air pump, the one used in the fish tanks.


April 09, 2020 at 9:02 am, Jaap Posthuma de boer said:

Air passed through oil has different properties, not the same product.


December 29, 2016 at 1:03 pm, Mohit said:

I read on a forum that this way the oil can cause most yellowing. Also that as it has already partly oxidised it will have an adverse effect on adhesion. Is this true? Because if it isn’t then I will try it for sure. Thanks.

Can someone please comment on this


January 18, 2018 at 6:02 pm, Michael said:

The oil acts as a glue and a very strong one given the best opportunity, giving it that best opportunity is the key. Slightly pre oxidising it will not change its strength in a significant way. Indeed an excess of oil will tend to promote the murky yellow colour always try and minimise that excess.


December 28, 2019 at 9:02 pm, Henri Ruukki said:

If I have understood correctly, the yellowing agents are actually removed by the sunlight in the process. This is, by accounts all through history, one of the best oil painting mediums.


January 24, 2018 at 10:51 am, xander calceta said:

Can i use any kinds of linseed oil for this procedure like boiled linseed oil for instance instead of refined linseed oil?


January 27, 2018 at 3:18 pm, Michael said:

HI Xander,

You can use any but the lighter the colour the less yellowing will occur.



October 23, 2018 at 7:05 pm, Charles Thornton said:

> Slight warning, “boiled” linseed oil is NOT boiled, it has drying agents added -such as cobalt compounds


February 25, 2019 at 2:23 pm, Simon Mathers said:


I was wondering can you do the same with nut oils?

Thank you,



April 30, 2019 at 1:56 pm, Michael said:

Hi there,

Yes, with nut oils


April 14, 2019 at 3:35 pm, Philip Fairbairn said:

This is very interesting. I read about this method about twenty years ago in a book. I didn’t get it then and now the way you explain it makes more sense.
Anywho, Im painting in the Flemish style and use CHELSEA linseed oil extra pale. I wonder what your thoughts are on using this oil if you have any I would be interested in reading them., Thank you for your time.


April 23, 2019 at 3:19 pm, Michael said:

Hello Philip!

Thank you for writing to me. I currently do not have any more content on this subject, however one useful tip which I always keep in mind is;

The more you stir it in the window and the longer its there in the light the thicker it will go.

Best wishes!



May 20, 2019 at 12:06 pm, mark said:

Just to clarify a point folks. This process will only worked with pure cold pressed linseed (flax) oil.


September 28, 2019 at 4:39 pm, SamNoelPearce said:

I have some 500ml of sun oil in one dark bottle that was full with no space for air for over a year. . . and some of the same batch I left in another bottle that was clear that I forgot about and recently found, that had been left for about a year in a box inside the studio in the shade and was half full of air and sealed…
It had coagulated and was crusty on the surface and throughout like porous lung tissue. . . yet the flax oil inside the mix was poured off into another bottle of the lightest shade (almost like a mild white wine colour) . . .
It seems that the trapped air has reacted (oxidised) with part of the existing Flax Oil in the abandoned bottle and the only thing left is a more refined version of the same… and much lighter, much like light machine oil for sewing machines. . . but I’ll use it for PAINTING FOR SURE. . .


December 06, 2019 at 4:05 pm, Michael said:

Hi Sam!

Sounds fun as long as it’s a light colour 🙂




January 23, 2020 at 6:49 pm, e said:

I have an additional question for this thread… I made a version with raw linseed oil I refined myself that had wonderful texture but was very ambar coloured. I am going to try again with a better quality refined oil like yours, but also have the option of lighter “bleached” linseed oil. I should add, my aim is an oil with drag that keeps strokes as best possible and dries more quickly. I have seen comments elsewhere that say bleached oil tends to be smoother and slower drying (I’m not sure why if it is supposedly sun-bleached, but if it’s true…), I thought using bleached oil -although lighter- may have a detrimental effect on the drag you get when you then sun thicken it quite a lot (which is what I’m looking for). What do you think? I know experimenting is the key but advice is always really helpful. Thank you so much for your time and amazing painting materials!


June 17, 2020 at 6:18 pm, Michael said:

Hi Elina,

We make a Pale Linseed Oil, already completely refined – This what you should use, your amber colour oil will make your whites amber!

Best wishes


May 05, 2020 at 12:33 pm, Tawanda Zindoga said:

Will Raw linseed oil work for the same purpose; the medicinal kind of linseed oil?


June 09, 2020 at 4:41 pm, Michael said:

The lighter the colour of the linseed oil, the greater the suitability it has for painting


May 16, 2020 at 10:30 am, Helen said:

Can you use cold pressed but unrefined linseed oil like the kind used to give to horses? Thank you.


June 09, 2020 at 4:41 pm, Michael said:

If you are trying to make the horse more artistic then, by all means, give it a try. However, if you are asking if you can use dark linseed oils when painting then I would advise strongly against it as it will make the painting go dark.


June 10, 2020 at 12:31 am, Noah said:

Hey Michael,

After making the batch, what are your recommendations on how to best store? How long is it good for?


June 17, 2020 at 6:17 pm, Michael said:

Hi Noah,

It’s good forever – best kept in an airtight container and not in the dark.

Best wishes and happy painting!


June 24, 2020 at 11:44 pm, Jon said:

Hi Michael,

Will sun-thickening work (first of all) and if it does, will it transmit the same properties to your safflower oil? Would that be a suitable medium for all your paints, not just the Titanium No.1?



February 16, 2021 at 2:00 pm, Michael said:

Hi Jon,

It should although more slowly, try it and let me know.


July 31, 2020 at 6:59 am, Bernice frederick said:

Good Day. My precious art teacher mixed raw linseed oil and genuine turps together (can’t remember ratio) and left it on a windowsill till thick. Would this work. I did a bottle back then, but it’s a rich amber colour so I’m guessing to not use it. Any thoughts would be appreciated


February 16, 2021 at 1:59 pm, Michael said:

Avoid raw linseed as it will make paintings go dark as that’s its natural colour, try pale linseeds I suggest you read up on sun thickened linseed oil. Putting turpentine in direct sunlight is not a good idea as it makes it go cloudy and it will never dry properly, this is because the water molecules have separated. Just put linseed in sunlight on the windowsill.


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