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Thursday, May 08, 2008

Linda Blondheim Art Studio Landscapes of the South

Gold Finch
4x6 inches
gouache on acid free mat board

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Painters Tip

This week I share quite a bit of information I have found on the web about various whites in oil painting. I would like to credit the authors but can't remember which sites I researched.

Titanium White - titanium dioxide (oxide)
Reflects 97.5% of all available light. The most opaque white, perfect choice for direct painting but difficult for color mixing because it takes so much color to tint Titanium. Titanium is completely inert, does not change by aging or normal chemical action, but it does require more oil to grind than other whites and can show some yellowing because of the darkening of linseed oil when it dries. It does not dry very quickly and is more Zinc white in this respect. Titanium White does not dry as hard as Zinc white eventually will, and consequently will make a more flexible film.

Flake White - basic carbonate of lead
Flake white has a heavy pigment requiring very little oil, and combines in time with oil to make a very flexible film. It is regarded as the most reliable white on which to build a painting. It can be applied more heavily than other whites with less danger of cracking than other whites. Flake white dries well and is a "warm" white. Note: Being composed of lead, Flake white is poisonous if absorbed into the body, but this does not happen by external contact.

Zinc White - zinc oxide
The most popular and transparent of the whites, it is also slow drying. It is a "bluish" (cold) white color, not nearly as strong and opaque as Titanium White and therefore can be very easily controlled. Zinc is recommended for scumbling and alla prima painting. Impressionists who painted directly liked Zinc White for its transparency and slow dry time. But Zinc's slow drying time and brittleness does not make it a good choice for general painting.

When painting in the indirect method you need to remember the fat-over-lean rule: always paint a more flexible layer over a less flexible one. With that in mind, the brittleness of paint films created with Titanium or Zinc whites make them less suitable for this method of painting than Lead white.

"Fat" refers to the fatty drying oil used as a binder and in mediums. A fatty layer of paint has more fatty oil (linseed, poppy seed, walnut, etc.) in it than does a lean layer, or one containing less fatty oil. To paint "Fat-over-lean" is defined as painting in layers of paint, which contain successively greater quantities of fatty drying oil.

The purpose of this method of layering oil paints is due to the fact that oil paints do not dry by evaporation, but by oxidation, during which time the paint film flexes and moves. By adding more oil in each layer of paint you insure that the lean under-layers will dry before the top layers to prevent cracking. Whereas a lean layer painted over a fatty layer would completely oxidize and become inflexible, causing it to crack when the underlying paint layer flexes during oxidation

Painting on a flexible support, such as canvas, creates flexibility within the structure of the painting, which can be damaging. Any painting on cloth, which received a blow (whether from being bumped from behind or dropped, etc.) will cause a certain type of cracking which is usually visible in a circular pattern on the painting's surface. There is only one way to attempt to avoid this. Paint in a series of daubs of color separated so as not to create a continuous paint film. the flexing support can then bend between the brushstrokes without cracking them. However, this style of painting is very limiting creatively.

Most artists desire to create a continuous paint film across the support and have, for centuries, done so in varying thicknesses of paint: thin wash imprimatura, covered with transparent shadows and bold, thick highlights, glazed with transparent glazes and scumbled with thin layers of translucent opaques. The key is in knowing the amount of fatty oil in each color. Each pigment has different properties, including particle size, which determine how much oil is required to turn it into a paste. Craftsmen of past ages, who ground their own paints, knew which pigments were high in oil and which were low. The underpainting would then be produced in lean colors and successive layers used fattier pigments, or else more oil (in the form of a medium) was added to altar the paint film's elasticity. Lead white is a very lean color - it requires very little oil to produce a paste for painting. Each pigment chemically reacts with the oil to effect drying. Lead white reacts in a way which speeds drying times by increasing polymerization. It should be used in underpainting or for painting over washes of color, but is more likely to crack if layered over a very fatty color such as a thick layer of umber or carbon black.

As a general rule earth colors, especially those containing heavy metals, dry faster than do organic or synthetic pigments, which have finer particle sizes.
Because of the yellowing of linseed oil, many artists and paint manufacturers throughout the ages have sought to use other binders or vehicles for grinding pigments into paste, especially lighter colors and cooler colors which may be effected by yellowing. Rubens and others of his day ground whites and blues in walnut oil because it yellows less.

Today, many paint manufacturers, creating paints for the direct painting methods of the impressionists and plein air painters, use poppyseed, sunflower, or safflower oils. However, none of these are suited to layering paint. Archivalists discourage the use of poppy seed oil because it is brittle and cracks more easily. Safflower is also not a good substitute because it never dries and is thus not truly a "drying oil." Most paint manufacturers using these oils add dryers to the mixture to force consistent drying. But there is little that they can do to prevent the inherent brittleness of these paint films. The very chemical within linseed oil that makes it yellow is also the thing that makes it flexible.

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