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Solvents The volatile essential

From Gum Turps to plain water solvents have many uses as you make paint both in the process of paint making and for cleaning up equipment afterwards. They are dealt with here in 4 main groups of which 2, water and turpentine are by far the most important.

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Warning Use with care
With the exception of water, solvents are flammable substances and particularly so in the form of confined vapors. Always use solvents with adequate ventilation, and be careful to avoid open sources of ignition. The risk increases as the strength of the solvent increases, but even solvents thought of as being safe to handle such as Grain Alcohol should be used and stored in a way mindful of possible harmful effects.

Also with the exception of water all solvents are toxic to at least some degree including the inhaling of vapors. Any artist who has experienced headaches after painting with oil paint in an enclosed studio is experiencing the toxic effects of Turpentine vapors. This is not recommended, and good ventilation is required when using these substances.

Water Cleaner as well as paint ingredient
Water is the only solvent that is used for making all forms of paint, although it is less likely to be used as a direct ingredient in oil paint, so much as as a cleaner.

As a paint ingredient.
Distilled water is the only form that water is ever added to paint mixtures. Ordinary tap water may contain impurities that can chemically react with, or discolor some pigments. Untreated water is also likely to contain microscopic life which can spoil paints, especially when stored for long periods. In the Renaissance artist's dealt with this in 2 ways. Firstly they collected pure water directly in earthen containers as it rained (and not off a roof) and also paint when not used in a very short time was discarded as not being fresh enough. Now that we use tubes spoilage like this becomes an issue. Egg tempera needs particular care in this regard as it is a food product and particularly prone to spoilage, so always use distilled water only.

As a cleaner.
Clean tap water is fine for cleaning equipment. Aqueous paints dried on equipment are best softened in hot water first and alcohol will usually dissolve aqueous mediums. Acrylic is always soluble in alcohol, and so long as your clothes are not an acrylic fiber, alcohol can always be used to remove water based paint from most surfaces including clothes With clothes it is wise to test first in case the dyes in the fabric are  also alcohol soluble or otherwise affected by the alcohol.

Clean oil based paint from equipment while still wet as oil based paints once dry are insoluble except in the strongest solvents. Use turpentine to dissolve the bulk of the paint, and then wash the residue of in warm soapy water, and then rinse in pure clean water. Metal tools need to be dried carefully so as to prevent corrosion.


Wetting agents Helping solvents work
Some pigments resist getting wet. This is particularly true of organic pigments. Alcohol and Turpentine are solvents that are already excellent wetting agents for oil based paints but water based paints need a hand at times too from an outside substance. Ox Gall is the traditional product for this and is readily available in any store that sells watercolor supplies. A product of the acrylic manufacturers is proving to be even more effective. It is sold under the name Surface Tension Breaker by Matisse.


Alcohol Aka Methylated Spirits or Grain Alcohol
For most purposes denatured alcohol, often called Methylated Spirit is suitable. In places where the denaturing includes noticeable dyes this is less desirable. Pure grain alcohol is available where the common denatured product is objectionable. 94% grain alcohol contains water but is fine in most cases. Absolutely water free alcohol is called anhydrous. Many jurisdictions require permits to use these non denatured alcohol's. Rubbing alcohol should never be used as it contains up to 25% water and various denaturants that are unsuitable for paint use.

Denaturants commonly found in Methylated Spirit include Methanol and Pyridine both of which are included to make the mixture less palatable for drinking. Methanol is more poisonous than grain alcohol but is actually a better solvent and can be substituted for grain alcohol where the denatured product is objectionable if suitable precautions are observed for handling this more toxic substance. Methanol is also called Wood Alcohol.

Alcohol can be used as a wetting agent for certain pigments such as those organic pigments that resist wetting easily when grinding. This alcohol should subsequently evaporate during the grinding process and not cause long term problems. Denaturants such as Methanol will likewise evaporate without problem, but some other denaturants including dyes may be more long lasting.


Turpentine The universal solvents for oil paints
Turpentine and Mineral Spirits have been known since Greek and Roman times but were made in small quantities for use in medications only. They were not adapted for use in paints until the Renaissance when large scale production methods were devised. It has been pointed out that the use of oil paint as an artist's medium began due to the introduction of volatile solvents as before then the paint was too difficult to handle and so was unpopular because of this.

Gum Turpentine
The smell of Gum Turps permeates the oil painter's studio and is attractive in a way that no other studio smell is. To hear painters talk of the smell of Gum Turps you would think they were addicted to it. Unfortunately in many cases that is literally true, at least mildly so, just as it is for those who regularly sniff other volatile substances such as glue.

Gum Turpentine  despite its attractive odor is toxic and should never be used without adequate ventilation and should never be used in open pots or jars. The practice of keeping dirty brushes soaking in open jars of Turpentine should be avoided. Despite the toxicity, Gum Turpentine is one of the least flammable of the volatile solvents.

Turpentine is distilled from the sap of various Pine trees. In old writings the word turpentine refers to oleo resinous substances that we now call Venice or Strasbourg turpentine. These turpentine's still contain the resinous element. It was only in the 19th century that the Gum Turpentine that we are familiar with was born when manufacturers started to distill the volatile portion from the resin (which is called rosin).

Gum Turps should always be fresh stock as it deteriorates with exposure to both air and light. There is no quality difference between the expensive product sold in small bottles for artist's and the far cheaper industrial supplies as they both come from the same source. However the industrial product is likely to be far fresher as it is sold in greater quantities.  Some of the larger hardware stores sell pure Gum Turpentine, and if you can access this supply it is an excellent choice, although be wary that it is not reduced with wood Turpentine which you can tell by smell.

Gum Turpentine is the only thinner and solvent that the artist can use for damar, as it does not dissolve well in Mineral Turpentine.

Mineral Turpentine
As a general solvent it is an excellent choice as it has few of the drawbacks of Gum Turpentine. It is cheaper and it does not deteriorate with time. It is also less toxic and is easier for those with allergies to use. Despite these advantages most artist's won't use it because either they don't like the smell or are not aware that it is just as good as Gum Turpentine as a solvent.

Its general properties are similar to Gum Turpentine with the exception that is cannot be used to dissolve damar or be used to thin paints that have a resin content.

Odorless Turpentine
Various substances are sold under this name from Mineral Turpentine to various Turpentine's distilled from various trees. Citrus Turpentine is one that is common these days. I am unaware of any investigations of any of these other than Mineral Turpentine by respected artist's materials authorities, although the manufacturers claim they are not problematic. Mineral Turpentine is fine to use but I am wary of the other products for the time being until independent testing is done that is relevant to artist's usage. As Mineral Turpentine is the least allergenic of these solvents and is known not to harm the paint film it should be the first choice for those who are allergic to Gum Turpentine, or wish to avoid Gum Turps toxicity. For those who are still affected by any solvent I would recommend investigating the many good features of Egg Tempera or other water based media.

Historic solvents.
Oil Of Spike Lavender.
This is quite different to Oil Of Lavender which comes from a different plant, Oil of Spike comes from the Lavendula spica which grows wild in Europe. Until the 19th century (when today's Gum Turpentine originated) it was the most common solvent used by oil painters. It is therefore found in many early recipes. It has the drawback that it retards the drying speed of the oil and it deteriorates quickly in air. Gum Turpentine or Mineral Turpentine are both superior products and should replace Spike Oil. It has been suggested that the only reason that it was more popular in early centuries was because as a common wild plant it was easy to make.

Venice Turpentine and Strasbourg Turpentine.
These oleoresins are used less as solvents than as resinous additives to paints. They have the benefit of imparting greater flexibility to oil films. They are considered relatively non yellowing and durable Strasbourg Turpentine was regarded in past centuries as superior but it is harder to find and is expensive. Venice Turpentine is conversely easy to get and cheaper. Neither is used in industry anymore and artist's are the only users of these Turpentine's. They have a good reputation in Egg Tempera when a egg-resin type of Tempera is desired. Mixed with stand oil Venice Turpentine makes an excellent varnish.

Go to Historic Pigments page


Stronger solvents 'Thinners'
For most making of artist's paints these stronger and therefore more toxic and dangerous solvents are never necessary and should not be used. They come with exotic names such as Xylol, Toluol, Benzol and N-Hexane. Automobile paints are usually thinned with substances such as these and are sold as 'thinners' for spray painting. Avoid their use unless you are experimenting with epoxy resins or other paints that require stronger thinners. They are more toxic than traditional solvents and very flammable. Experiments with these sorts of paints should not be conducted in the average studio but in appropriately equipped workshops and garages.
                     
Go to Safety page




References
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Parkhurst, D B,    The Painter In Oil   1898 (Lothrop, Lee & Shepard)
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Roy, A      Artist's Pigments: A Handbook Of Their History And Characteristics,      1994 (Oxford University Press)
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Theophilus,   On Divers Arts,    1125 (Dover)
Various,    Encyclopedia Britannica,    fifteenth edition 1981  (Encyclopedia Britannica, Inc)
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Vasari, G,   The Lives Of The Most Excellent Painters, Sculptors And Architects,    1568 (Penguin Classics)


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