Oil paints are formed by saturating pigment (finely ground coloured compounds) in boiled linseed oil. As the paint sets, the oil accumulates on the surface and forms a glaze over the pigment. This acts as a barrier protecting the pigment and adding brilliance to the colours, since they appear wet under the oil glaze.
We cannot determine when oil paint was invented because even cave men mixed crushed coloured clays and charcoal with animal fats and oils, to create a rudimentary oil paint for their cave walls. Long before white settlement, the New Zealand Maori, a stoneage Polynesian race were painting their elaborate wood carvings with oil paint made from fish oil and either red ochre for a red colour or lime from shells burnt in their cooking fires for a white oil paint. They used it not only for colouring their carvings but they also understood the paint protected the wood from rot.
The Maori was using oil paints long before
contact with European explorers. This Maori
wood carving is sealed and preserved with
red ochre oil paint. The teeth are highlighted
in white oil paint made from ash and fish oil.
The New Zealand Maori created a complete art form called Kowhaiwhai for the art of oil painting and it was used to symbolise historical events, family lineages and to distinctively decorate their large meeting house or "Whare" both inside and out.
The rafters of this Maori tribal meeting house or "Whare" (pronounced "forry")
are decorated in kowhaiwhai, painted with oil paints made from shark oil mixed
with red ochre (for reds), charcoal (for black) or shell lime and ashes (for white).
This settling of oil out of the paint forms a protective barrier and makes oil paint an excellent preservative for wood and
cloth. It also makes oil paintings easier to clean since the outer glaze with its trapped dirt and grime, can be stripped off the painting,
without losing any pigment. This is done using a special solvent solution and working in small areas at a time.
Some pigments like Ultramarine change colour if they become acidified. The picture cleaning fluid also contains reagents to
de-acidify the pigments and restore their original colours. This can produce some surprising results.
After cleaning a family heirloom oil painting for a customer, I came back the next day, horrified to find a large castle
perched on a hill that was bald yesterday. How do you explain that to a customer?
The painting had been in the family for a century and no-one remembered a castle there. It was the family's home village in
England and no-one could recall a castle ever being on that hill either. Finally an elderly village historian recalled some ruins that had
been removed when she was a small child, to build a pier. Investigations revealed there was a castle on that hill that had been razed over
400 years ago. The artist had included it in the picture and to capture the colour of the stone in the distance, had used a mixture of the
sky colours with ultramarine. Over the years the ultramarine pigment (ground Lapis Lazuli) has become acidified and lost its colour leaving
the only the sky colours - a disappearing castle. Cleaning the ages of grime off the painting with my own special picture cleaning fluid had
slowly de-acidified the paint, over night returning the ultramarine to its former blue - the castle re-appeared.
Several pigments will alter colour over time and are marked as "Fugitive" on the tube, if you are using a good quality oil paint. With modern technology these pigments are being replaced with "frits" or pigments reacted with silica and ground to produce a less reactive pigment.
Several pigments are highly toxic. Today these pigments are usually "fritted" to make them insoluble and therefore non-poisonous under normal conditions. However if you are handling or restoring old paintings, be aware that they will contain several toxic pigments. Most common is lead. Many colours use oxides and carbonates of lead - flake white and Naples yellow are common examples. Other toxic examples are the vivid reds and strong yellows that are produced by compounds of cadmium. This is a particularly insidious poison because it takes ages to show as it replaces the calcium in your system causing a condition known as Minimata Disease.
However by far, special mention has to go to Prussian Blue and Monastrial blue. These pigments were actually used as murder weapons!
Dated 1479, this illustrated manuscript of a Dutch scribe still
retains it's brilliant hues. The scribe's bright blue garments are
coloured with pthalocyanine blue (Monastrial Blue)ink. Copper
chromium compounds form the greens and iron oxides the
In the Middle Ages, in monasteries, monks experimenting with chemicals discovered as intense brilliant blue pigment called Pthalocyanine, a toxic compound of cyanide. It became the source of nearly all blue inks used for illuminating holy manuscripts. Today it is more commonly known as Monastrial Blue. Because of it's toxicity, it was found to be the cause of many untimely deaths of both scribes and cardinals alike. The former; from accidental ingestion and the latter from career opportunists eager to acend the promotional and political ladder within the church. Scribes were readily identifiable within the community by the telltale blue stain on their thumb and index finger from this ink.
Nowadays Monastrial Blue and Prussian Blue, both use the cyanine compounds but in modern oil paint (as well as acrylics and watercolours) it is compounded with other substances to make it insoluble if ingested. In some preparations the cyanine compounds can be reconverted into soluble (and therefore toxic cyanine dye) if they come in contact with acids like vinegar, lemon juice or wine.
Generally when working with old documents we should wear gloves so contact with these toxins is rare but keep these toxic pigments in mind when working with old artwork and never forget that also applies to the frames too!
This old frame was sealed in red lead primer and the white
moulding putty was also found to contain a high quantity of white lead.
Many were sealed at the corner joints with white lead and it was common to undercoat wood with red lead primer as a proof against borer. Lead is an accumulative toxin that is highly carcinogenic (cancer causing), easily absorbed into the body's chemistry and very difficult to remove. Only recently have we come to appreciate the full toxicity of lead compounds so many old items will contain lead derivatives that would classify them as hazardous today.
Here's an example of the dramatic difference a cleaning can make to an old oil painting. This painting is only 70 years old but it had hung above an open fireplace in a country hotel in the UK for more than 40 years, exposed to a constant cloud of cigarette smoke, wood smoke and humidity. When it was so grimy that it became an eyesore, it was abandoned in the attic for another 30 years then given to one of the grandchildren as a worthless piece of junk.
Before and after cleaning - when 70 years of grime are removed.
It was fascinating to watch the transformation in this painting as the grime and creosotes came away with the oil glaze to reveal the picture. But it was truly amazing to come back the next day and see the colour change as the sea turned from greys to blues. The painter had used Ultramarine in all his colour mixes and overnight the paint slowly de-acidified. As the blue returned to it's original hue, the picture developed shadows and tone we had not noticed when the grime was removed.
After cleaning and washing to make sure that no reagent was left on the paint surface, the picture is then air dried and over the next few weeks the stripped oil glaze is replaced with multiple applications of a special mixture of oils. Finally the painting's stretcher frame was treated with linseed oil for preservation and to discourage borer. The canvas was re-stretched and put back in the original frame, (which we also restored).
Some art suppliers sell an oil painting cleaner solution which you can use to clean paintings, yourself. This is not usually a problem if the painting is in good condition and is not very old. However when a painting is over 50 years old, time ravages the canvas as well as the paint and you can easily end up damaging the canvas, causing it to stretch and craze the paint or worse - let go and tear. Paintings over 30 years old are best left to the experts.
Not all paintings are painted on stretched canvas. Many of the oldest oils were painted on wooden panels, for example Leonardo Da Vinci's Mona Lisa is painted on a poplar wood panel.
Leonardo Da Vinci's famous oil painting
is painted on a poplar wood panel.
Oil paint is a natural preservative for wood, forming a barrier against moisture and a repellent for wood eating borers. Even today many artists use oils on primed wood panels. With today’s technology artists have a range of wood products available as substrates. Although less prone to damage, accidents do happen but repairs are possible, though much more difficult and should be left for the expert.
This seascape in oils on a wood panel is part of a family trust collection and was damaged in transit. A very distraught client delivered the pieces to me with grave doubts it could be restored.
"Good Sailing Weather" a severely damaged original oil painting on wood panel before repairs began.
This is MDF board - a wood fibre board that separates into layers when it breaks. This means the board in thicker and weaker at the site of the break due to delamination. The fibres that protrude from any break in a wood panel, never fully match up again to provide a clean joint so the first stage was to trim the board to form a good joint. A diluted solution of epoxy resin is then applied to both joint surfaces, to steep into the wood and rebind the layers where they have delaminated. Now we have two surfaces that can be rejoined.
The rejoined corner is stabilised and re-laminated then joined and filled with
epoxy resin and wood fibre. The excess is milled off once the repair has fully
cured. This picture of the milling process, taken from the back of the painting
shows the milling finished at the lower left half of the join.
The surfaces are now joined and bonded with epoxy resin. To provide the proper substrate for the oil paint that will cover the repair, wood fibres are added to the resin. Once fully cured the excess resin and wood fibre is milled off back to the original board thickness.
The painting "Good Sailing Weather" is rejoined. Now we have to fill the
joint and match the paintwork. Here comes the hard part!
The back of the picture is finished and will be stronger than the original board. We now are left with a groove in the front that has to be filled. This is done with coats of a special ghesso and left to thoroughly dry. Tiny samples of the paint are tested to determine the pigments for the paint rematching process.
The Finished repair on "Good Sailing Weather is undetectable even close up.
Finally, we rematch the oil paint. This is a difficult process on this painting because the artist used a wide range of colours on the palette and the entire painting is done with a palette knife. The colours had to be built up in layers exactly like the artist had done, to match the surrounding area of the painting.
No two repair jobs are the same and it is extremely difficult to quote a price based on time and materials. Often it is not until the work is removed from its frame, unstretched, properly cleaned and treated, that you have a full idea of what materials will be required or how long the job will take. We quote a price at the start and stick to that quote regardless. Sometimes we come out on top - sometimes we don't but the important result is that the artwork will still be around for generations to come when it is restored properly.