255: Using Calcite Sun Oil–An Interview with Louis R. Velasquez

RECENTLY I needed a thicker oil medium and have been experimenting with sun oil. So far I’ve enjoyed painting with a mixture of very thick sun oil and Gamblin Gel. It can be applied thickly yet stays put on the canvas–it doesn’t drip or sag like many linseed oil mediums.

I came across a DVD by painter Louis R. VelasquezPainting with Calcite Sun Oil, that recommends using flax seed oil and purifying the oil before sun thickening. After watching the video I’m convinced that purifying, or removing the mucilage, is a necessary step in making proper sun thickened oil.

Closeup of oil paint with Calcite Sun Oil medium

Linseed oil is a wood protectant and traditional paint binder. Flax seed oil is typically found as a nutritional supplement in health food stores. Linseed and flax are genetically similar plants. The difference is not in the oil but in the way the oil is obtained from the seed. Food grade flaxseed oil is cold-pressed, whereas modern linseed oil is extracted using chemical solvents and high heat. Flax was bred for making cloth and linseed was bred for high oil content but their oils are identical. Velasquez recommends using food grade flax oil that is unrefined, unfiltered, organic, and has no additives such as lignans.


According to Velasquez you should make sun oil with food grade flax oil because it has not been subjected to high heat and chemical solvents that degrade the oil making it unsuitable for archival painting techniques.

The DVD Painting with Calcite Sun Oil is over an hour long and details a variety of mediums and tips for how to make sun oil as well as Calcite Sun Oil (which I have referred to as putty, although I agree with Velasquez that it’s a harsh sounding word). My favorite part was how to remove the mucilage from flax oil and the random tips such as using a white porcelain tray instead of a glass one to speed thickening, and avoiding using a metal cookie sheet because of later problems with wrinkling. Another fascinating tip was using milk as a fixative and using a straight palette knife for painting (which amazingly I’ve never tried).
I contacted Velasquez with a few questions and he graciously agreed to an interview.

BRAD TEARE I found your DVD fascinating. Thank you for putting the information into an easy to understand format. I previously read about similar ideas but your video shows why it’s important to invest the time to purify the flax oil and why you should start with food grade oil. The footage of the cleansed oil in the bottle versus the uncleansed oil was very compelling. The purified oil was so clear and fresh looking. You stated that you discovered how to use psyllium husk and alcohol to cleanse oil from Francisco Pacheco, the teacher of Diego Velasquez. Did you translate the recipe from the original manuscript?

LOUIS R. VELASQUEZ  Thank you for the opportunity to share CSO ( Calcite Sun Oil) with you and your readers. In your intro, you mention the word “putty” as descriptive of Calcite Sun Oil. The word putty is not only harsh–it is misleading. 

Historically speaking putty was a mixture of chalk powder and cheap industrial linseed oil (certainly not the superior oil of the Old Masters I describe as all-important to archival oil painting). That obsolete putty mixture of cheap linseed oil with chalk had its use as a glass window glazing compound. In olden days it’s purpose was to keep the rain outside the house. Today we use modern silicone mixtures for our windows.

We fine art oil painters must seek to elevate the vocabulary of our honorable profession. For instance, Rembrandt made oil paint from various colored dirt, yet we don’t use that term, we call them earths. Therefore, I ask artists not to use the term putty (window glazing), nor goop (glue), nor gunk (radiator scum).

Regarding the use of psyllium husk for the removal of the mucilage from the unrefined flax oil I must correct you. I am the originator of using psyllium husk in the cleansing of the oil. You will not find it mentioned in any of the literature of oil painting, ancient or modern.

It happened this way: I’m an older man, I just celebrated my 72nd birthday, and with age comes many health issues. One of mine was poor digestion and my doctor recommended I take Metamusil, an over-the-counter laxative. I read the label and learned it was simply psyllium husk with some sugar flavoring!

One day I saw how a small amount absorbs a huge amount of water. I combined that observation with what I had learned from studying the oil cleansing method of Velazquez’ teacher, Francisco Pacheco, El Arte de la Pintura (1649). Pacheco used liquor and lavender flower buds. In my testing I observed the liquor extracts spike solvent from the lavender buds and fills the oil with hazardous solvent. Since my goal was to create a completely safe, solvent-free oil painting method I had to eliminate the use of the lavender. Luckily, I saw the importance of the psyllium husk. Still, I give full credit to Pacheco for his recipe. He was my guide.

BRAD I like the fact that you use food grade ingredients, which makes the formulas more affordable. You describe how to mix the psyllium husk–which you suggest buying at a health food store–with 80 proof alcohol to make the cleansing mix. I assume you buy the alcohol at a liquor store. Adding the alcohol seems like the most expensive step of the process. Do you have a source for the alcohol that is less expensive? Is there a brand of 80 proof alcohol that you recommend?

LOUIS The food grade flax oil is much less expensive than the art store alkali refined industrial linseed oil. I buy a quart of Barleans Flax oil for about $38 a quart. The dry psyllium husk is low cost and a small bag goes a long way. You are correct–the liquor is the most costly. Basic Liquor is made up of two parts, water and ethanol. For the psyllium husk to work correctly it needs water–that’s why I recommend only 80 proof liquor. The proofing is half the number. This means that 80 proof is only 40% ethanol and the rest is 60% water.

We in the US have access to lots of cheap liquor and one can use any clear liquor–be it whisky, vodka, gin, etc. But residents of many other countries pay a very high tax for liquor. After many requests for help I embarked on finding a non-alcoholic method to remove the mucilage. This method is on my website. It is called the CSO Psyllium Husk-AirPump (Velasquez-Tavenier) Method. My friend, Daniel Tavenier, from The Netherlands, inspired this new easy, non-alcoholic method. I will give an important warning: If you decide to use alcohol, do NOT use denatured alcohol (also called rubbing alcohol). It’s fumes are exceedingly dangerous to your eyes.

BRAD You mention that you use powdered or whole psyllium husks to add to the alcohol. Do you have a preference?

LOUIS There is no difference. They both are effective. My DVD is a bit outdated now, and I must upgrade it, so I advise readers to read my website for the latest information.

BRAD Have you ever made sun thickened walnut oil? Does it need to have the mucilage removed using the psyllium/alcohol method?


LOUIS I also tested raw unrefined walnut oil during my experiments. It has just as much mucilage as does the flax oil. You can use the very same mucilage cleansing methods as with the flax oil. Your readers must take care with the oil they buy, regardless if it is walnut or flax oil . Many manufacturers add anti-oxidants to their oil as a way to keep it sweet tasting. This additive causes the oil to dry very, very slowly. Common anti-oxidants are Rosemary, Vitamin E, Tocopherols, Polypherols. Even Barleans sells a flax oil for pets and it has antioxidants added. Many walnut oils contain added vitamin E.

BRAD I assume that the bleaching and thickening of the oil takes place at the same time. Is it possible to thicken the oil too much? Can it be bleached too much?


LOUIS The flax or walnut oil thickens when exposed to oxygen. If the jar is tightly capped, the thickening stops (if the jar is filled to the top). So yes, the oil can be thickened to excess and it becomes difficult to use. In that case you can add a non-thickened oil to the thickened oil and create an oil with the advantages and disadvantages of both. You can place both oils in a jar, place the jar outside in the hot sun to thin and mix them, or gently heat the jar in a double boiler of boiling water. A little shaking is needed.

The oil cannot be overly bleached. In fact, when the oil is exposed to direct UV sun rays for several weeks it becomes water clear. Then once inside the house it gets a straw color. The test is to put one drop on a pure white ceramic plate and rub it in. You will see it is completely non-yellow and colorless and it will remain colorless.

BRAD I noticed you didn’t put a plate of glass over the white ceramic trays with the cleansed oil inside for thickening. Most other methods use a plate of glass over the top. Is there a reason you don’t?

LOUIS I used to do that for years using a glass sheet and spacers for air. Then one day–since I live in sunny California with no chance of rain in summer–I discarded using the glass sheet. But if there is a chance of moisture I recommend covering the oil when it is outside. The oil gets full of bugs, leaves and dust, but these are easily filtered out.

BRAD When you described the Calcite Sun Oil mixtures (sun oil with chalk) I was intrigued by the terms Aguado, a thin calcite sun oil mixture, and Espeso, a thick mixture. How thick can you get the Espeso? When it gets thick is it completely opaque?


LOUIS I first heard of adding chalk (Calcium Carbonate CaCo3) to oil paint in 1988 when I bought the first edition of the book on Rembrandt published by the London National Gallery, which scientifically studied Rembrandt’s paint. Rembrandt actually used a chalk-oil mixture as a paint. He created thick impasto translucent bodied glazes with it.


Chalk is only one form of calcium carbonate. Other forms are calcite, marble, aragonite, and limestone. When chalk is mixed with hide glue it is pure white. The Old Masters called this gesso  as we still do. If the chalk is mixed with oil it is 98% transparent if the layer is thin. When it is made into a thick impasto it is opaque. When mixed with tube oil paints it makes the oil paint translucent giving it vibrancy.

BRAD If an artist could only afford either the Calcite Sun Oil DVD or the book which would you recommend?


LOUIS I recommend them buying the book, and especially the digitally downloadable format. The reason is that the print copy has no index but the digital version does. It is also cheaper AND I will send every book buyer a FREE copy of the DVD via US First class post–at no cost. The instructions are on my website.


BRAD Thank you so much for both the information in your video as well as sharing your ideas with the readers of Thick Paint! We really appreciate it.


LOUIS I am grateful to you and your website. I’m on a mission to make oil painting safe for all persons. Today, some artists are teaching CSO. One lives in Australia, one in Puerto Rico, one in Brooklyn. Others are indicating interest. You are helping by publishing this wonderful method. Every artist deserves to know the CSO/EMULSIONS method of safe oil painting. Thank you. –Louis Velasquez , San Diego, California

Thank you, Louis for your unique contribution to the technique of oil painting.

Brad Teare –October 2015

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Updated: 27th September 2020
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