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Auxiliaries Fixatives

When and how is retouching varnish used?

Use of retouching varnish

Retouching varnish (sometimes also called intermediate varnish) is used to revive sunken-in (matt) areas and provide temporary protection (temporary final varnish) of oil paintings not entirely dry.

Retouching varnish during the painting process:

Sunken in areas may occur while painting: the paint becomes matt and the intensity of the colour reduces. This cannot be avoided and is caused by a combination of the colour used, the type and amount of thinning agent added and the absorption of the ground.

The amount of oil in the paint as well as the amount of solvent that is added can vary per colour. If the paint contains relatively little oil,  some of which is absorbed by the ground, the colour may sink in.

It is now difficult to assess the colour harmony of the painting. Making the right decision on how to continue painting now becomes a problem. Treating the sunken-in areas (once they are thoroughly dry to the touch) with a very thin coat of retouching varnish restores their gloss and colour. If the sunken in areas are very absorbent it may be necessary to repeat the procedure (once dry) in order for the gloss and colour to be of a sufficient level.

The varnish dries in a few hours and leaves a porous film which in turn gives suitable adherence for a following coat of paint.

Please note: It is very important to apply retouching varnish very sparingly, as the paint, not yet completely dry, may dissolve in the solvent of the varnish. Preferably apply with a spray can.

Retouching varnish as provisional final varnish:

The retouching varnish can also be applied as a provisional final varnish to give the painting an even gloss and as a protection against dirt.

As the varnish (in a thin coat) is porous, the drying process of the paint can continue.

Please note: For this application it is highly recommended that the painting is left to dry for at least several months. Even if the paint is dry to the touch before then, the paint underneath will certainly not be. The solvent of the varnish would penetrate the lower layer and bring the oil that is not yet dry to the surface. If this happens the painting can remain tacky for many months, and contaminations will stick to the paint.

When fully dry, the final varnish can be applied over the retouching varnish.

The retouching varnish remains tacky, what could cause this?

A common mistake when applying retouching varnish is to apply it too soon or excessively.

The solvent in the varnish, if applied on oil paint that has recently become dry to the touch, would dissolve some of the oil in the paint which will lead to the oil reaching the surface, forming a sticky layer. If the retouching varnish is used as an intermediate varnish which is then painted over again, this will be no problem.

If the retouching varnish, however, is applied too soon as a provisional varnish the same phenomenon will occur, resulting in the exterior of the paint layer consisting of a mixture of oil and resin. This layer will stay sticky for months and patience is the only solution here.

To avoid this, it is advisable to wait for several months for the paint to dry out further before applying the varnish; for a very thin layer of paint, this is at least a month.

Moreover, it is very important to always apply retouching varnish very sparingly. The more varnish, the more solvent will be applied, thereby increasing the problem. What's more, only thin layers of retouching varnish are sufficiently porous to enable the adherence of subsequent paint layers (intermediate varnish) and the penetration of oxygen for the continued drying process of the paint (provisional final varnish).

Which varnish is suitable for acrylic colours?

Amsterdam Acrylic Varnish has been specially formulated to produce a durable finish to acrylic paintings.

The varnish consists of a solution of acrylic resin in white spirit and turpentine oil, is available glossy and matt and once dry forms a flexible film.

Amsterdam Acrylic Varnish Matt is matted with silicas (similar to pulverised glass) and must be shaken well before use. For a good adherence it is recommended to wipe an acrylic painting with white spirit before varnishing.  

Can different varnishes be mixed with one another?

Yes, glossy and matt varnishes of the same type* can be mixed in any ratio to bring about the desired level of gloss.

When applying a varnish that contains a matting agent the last action should be to brush the varnish in a single direction to achieve an even matt finish.

 

* The same types are: Acrylic varnish matt and gloss or picture varnish matt and gloss.

How do you apply varnish using a spray can?

Preparation:

  • Ensure that the paint is fully dry; with thin to normal layer thicknesses this is up to approximately one year, with thicker layers this can be several years. 
  • If a painting that is already a few years old is going to be varnished, the surface of the painting is first cleaned with a cloth with some white spirit. This removes dirt from the canvas and opens the paint film somewhat. The varnish will then bond better.

Steps invarnishing:

  • The matt and the satin contain matting agents that fall to the bottom in the varnish and therefore have to be shaken well before use.
  • Ensure that both the painting and the varnish are at room temperature.
  • It is best to lay the painting flat (with ample space on a piece of cardboard or newspapers).
  • Do not hold a spray can horizontally (do not point downwards) but spray forward so that a mist of varnish descends upon the painting. 
I have heard that you may only apply a final varnish after a year. Is it really not possible to do this any earlier?

No, this cannot be done any earlier unless the paint film is very thin.

An oil painting of normal thickness can be varnished after approximately one year, very thin layers several months earlier, and thicker layers only after several years.

PLEASE NOTE:If the varnish is applied too early then there is the risk that the solvent of the varnish will dissolve the oil paint that has not yet dried, and bring this to the surface. If this happens, the painting may remain sticky for many months, even years, and it would be difficult to stop dust adhering.

Does a provisional final varnish have to be applied onto an oil painting?

It is not necessary to apply a provisional final varnish, but this may be desired if the painting shows any signs of differences in sheen and is exhibited before a final varnish is applied. What's more, the paint is then protected against dirt.  

Must an oil painting be varnished? For how long must a painting dry before a final varnish can be applied?

Oil paintings – reasons and times for varnishing

Oil paintings must be varnished.

Varnish protects against ageing and dirt. When: after a drying time of at least 1 year.

Oil colours are a chemically drying (oxidative) paint; the oil dries through absorbing oxygen from the air. This helps to link the molecules together in chains. (Ultraviolet) light is necessary to provide the energy for this. The chemical drying of linseed oil takes much more time than the physical drying of the other types of paint.

Depending on the thickness of the layer and the type of pigment, the paint layer is dry to the touch in approximately one to six weeks. The entire film is completely dry between six to twelve months. Very thick layers may even take several years to dry.

Even then the uptake of oxygen does not stop; the ageing process now starts. Once the paint is completely dry it is therefore advisable to treat the painting with a final varnish. This helps to slow down the oxygen uptake and consequently the ageing process as well.

It is also important that the varnish protects the paint against dirt. Dirt and deposits in the course of time can nestle not only on the paint but also within it. If a painting is varnished, the varnish layer including the dirt can be removed without damaging the paint.

To ensure the durability of the paint layer, a painting may only be varnished once the paint is completely dry. It is not necessary to apply a provisional final varnish, but this may be desired if the painting shows any signs of differences in sheen and is exhibited before a final varnish is applied. What's more, the paint is then protected against dirt.

Does a painting made with Cobra water mixable oil colours have to be varnished?

Yes, this final varnish slows down the oxygen absorption and consequently the ageing process. This determines the eventual degree of gloss as well as protecting the paint from atmospheric contamination. 

Cobra water mixable oil colours dry like other traditional oil colours through the absorption of oxygen, which is a chemical process. Once the paint is entirely dry this oxidation process does not stop but continues in an ageing process. Eventually this can be visible as crackle. Once the paint is entirely dry (with layers of normal thickness this takes approximately one year, with very thin layers several months less, and with thicker layers several years) it is advisable to apply a final varnish. The oxygen absorption and consequently the ageing process are slowed down.  

What is a dammar varnish?

Dammar varnish is a natural tree resin dissolved in turpentine and is practically the only traditional varnish that is still used today.

Dammar varnish gives a high gloss. May show signs of ageing after some time such as yellowing and crackling.

Dries in a few hours.

How can an old varnish layer be removed?

Please note:If a painting was varnished before it had time to completely dry, the paint beneath the varnish will remain soft for quite some time, as the varnish layer will have sealed the paint from oxygen, making it difficult for the paint to continue drying. In this case, should the varnish be removed the paint would also be able to (partially) dissolve.

When removing old varnish layers, care must be taken to prevent any problems during cleaning.

Step 1:

Take a flat brush of a few centimetres wide, dip it into white spirit (use white spirit 090 ONLY) and brush it over a surface area of around 15 x 15 cm.

Step 2:

Wait until the varnish begins to swell. In the meantime, rinse the brush and repeat the procedure over the swollen varnish. This will now partially dissolve in the white spirit contained in the brush.

Step 3:

Continue the procedure with a rinsed brush until all the varnish on this area has been removed.

Step 4:

You can then treat the next area.

Please note: Once the varnish has been removed it will appear as if there is a white film on the painting. This disappears as soon as a new layer of varnish is applied.

the Amsterdam acrylic varnish also suitable as a final varnish for oil colours?

Our Amsterdam acrylic varnishes are also suitable as final varnish for oil colours, but do have slightly different properties.
- The gloss is somewhat different
- They are more thermoplastic
- They are more flexible

Differences between the Talens Acrylic Varnishes and Picture Varnishes

The Acrylic Varnish (glossy 114 and matt 115, for both oil and acrylic colours) is a final varnish, but does not have the same properties as the Picture Varnish (glossy 002 and matt 003).

The Acrylic Varnish is a solution of acrylic resin in white spirit, the Picture Varnish a solution of low molecular weight resin in turpentine (in the spray can white spirit).

Both types of resin do not yellow.

The 002 is glossier than the 114, the 115 more matt than the 003 (glossy and matt varnishes of this type can be mixed with one another to the desired degree of gloss).

The matting agent in the 003 consists of waxes that are dissolved in the turpentine; in the bottle the varnish appears crystal clear, but once dry shows an eggshell gloss.

The matting agent in the 115 consists of silicas (similar to pulverised glass); this varnish must be shaken well before use as the matting agent sinks to the bottom of the bottle. In the spray can the matting agent for both varnishes is silica.

For an even (matt) degree of gloss a varnish that contains a matting agent and that has been applied with a brush has to be brushed in one direction. The Acrylic Varnish forms a more flexible film than the Picture Varnish. This is of particular importance when using on acrylic colours, as this paint also forms a flexible layer.

Before a final varnish is applied a very thin layer of oil paint must have dried for at least six months, a layer of normal thickness one year, and thicker layers several years. If a dry layer of oil paint contains a lot of oil, it is advisable to wipe it with white spirit before varnishing to ensure good adherence.

The Picture Varnish Matt contains white floccules. What causes this? Can I still use the varnish?

The matting agent in Talens Picture Varnish Matt is a type of wax that has been dissolved in the solvent and flocculates at low temperatures. By warming the varnish ('au bain marie' or under a hot water tap) the matting agent is evenly dissolved again and the varnish can be used again.  

Auxiliaries Mediums

Acrylic mediums are white. To what extent is the colour of the paint influenced?

The binder for both acrylic paint and acrylic mediums consists of a dispersion of acrylic resin particles in water. As long as the binder contains water, the binder is white. When all the water has evaporated after drying, the acrylic resin particles in the binder form a continuous colourless transparent film and the white will have disappeared.

This explains why the acrylic paint colours become darker as they dry. When mixed with a medium, the wet paint therefore also becomes a little lighter; once dry the colour is the same as pure dried paint.

Can I also add Cobra painting medium directly to the paint?

Cobra painting medium can be added directly to the paint.

This makes the paint not only thinner but also fatter. Painting medium increases the durability of the paint.

This allows the artist to work according to the "wet-on-wet" principle; painting is continued as long as the paint is wet. If desired the medium can be made less fat with water; just like the paint, Cobra painting medium can be mixed with water.

Cobra painting medium can be used for layered painting. A next layer can only be applied once the previous layer is dry enough to ensure that it will definitely not dissolve.

In connection with the final durability of the paint film, layered painting has to follow the rule of 'fat over lean': each subsequent layer has to contain a little more oil.

Water makes the paint leaner, medium makes the paint fatter. The first layer can be thinned with water. The next layers are thinned with a combination of water and medium. As the mixture contains increasingly less water and more medium, each paint film becomes increasingly fatter.

How much medium can be added to the paint?

Acrylic Medium, Gel Medium, Heavy Gel Medium and Extra Heavy Gel Medium can be added to the paint unlimitlessly. Only the Amsterdam Acrylic thickening medium must be added in very small amounts.

What are the possible applications of Cobra painting paste?

Cobra painting paste is a colourless and water mixable medium that can be mixed in any proportion with Cobra water mixable oil colours.

The thickness is the same as that of the paint, and so the paste can be described as a water mixable oil paint without pigment.

Cobra painting paste has various applications:

  • Increasing the amount of paint. Cobra painting paste can be mixed with the paint in any proportion. So for the Impasto techniques of more expensive colours more paint can be made without any change in the colour. The more paste that is added, the more transparent the result; this however is not, or hardly, visible in heavy layers, depending on the type of pigment.
  • In combination with transparent pigments, transparent layers can be added with a glazing effect. 
  • Decreasing the tinting strength. The tinting strength of a colour will decrease, proportionate to the amount of paste that is added. This can particularly be relevant with the alla prima (wet-on-wet) technique, if colours with a strongly different tinting strength are mixed on the painting. By adding more Cobra painting paste to a stronger colour, its dominance will be reduced.   
What is a siccative?

A siccative is a solution of metal compounds that is used to speed up the chemical drying process of oil paints.

Use it very sparingly and minimise its use.

Read more 

Can a siccative be added in unlimited amounts?

In general, the use of siccatives should be kept to a minimum. Apart from the drying process, the addition of a siccative also speeds up a painting's ageing process.

To avoid problems, never add more than 2% Siccative Courtrai to the paints and never more than 5% of Siccative Harlem. In general, the use of siccatives should be kept to a minimum.

What is the difference between the light Siccative Courtrai and the dark Siccative Harlem?

The drying of oil paints can occur on the surface and deep in the paint itself. Depending on the metal compounds that make up a siccative, either the depth drying or the surface drying will be stimulated.

The light siccative, Siccative Courtrai, increases the drying in depth in particular, whereas the darker Siccative Harlem increases the surface drying.

When can I use an acrylic medium?

Mediums are used to change the properties of the paint, such as thickness, gloss, flow, drying time, transparency and durability.

A lot of painters only use water with acrylics, but this does not always produce the best results. Mediums can be used to achieve better and more durable results with less paint.

The addition of too much water can separate the pigment in the paint from the binder; the pigment is then unprotected on the painting and may run.

Oils, primers and solvents

What are the possible applications of Cobra painting paste?

Cobra painting paste is a colourless and water mixable medium that can be mixed in any proportion with Cobra water mixable oil colours.

The thickness is the same as that of the paint, and so the paste can be described as a water mixable oil paint without pigment.

Cobra painting paste has various applications:

  • Increasing the amount of paint. Cobra painting paste can be mixed with the paint in any proportion. So for the Impasto techniques of more expensive colours more paint can be made without any change in the colour. The more paste that is added, the more transparent the result; this however is not, or hardly, visible in heavy layers, depending on the type of pigment.
  • In combination with transparent pigments, transparent layers can be added with a glazing effect. 
  • Decreasing the tinting strength. The tinting strength of a colour will decrease, proportionate to the amount of paste that is added. This can particularly be relevant with the alla prima (wet-on-wet) technique, if colours with a strongly different tinting strength are mixed on the painting. By adding more Cobra painting paste to a stronger colour, its dominance will be reduced.   
Can Gesso be used over a Cobra painting?

Oil colours have a fat and smooth surface, on which the Gesso does not adhere properly.