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ISOLATION COATS

This Application Sheet discusses various isolation coat recipes and how best to apply them.

DEFINITION

An isolation coat is a clear, non-removable coating that serves to physically separate the paint surface from the removable varnish. The isolation coat serves two purposes:

1. To protect the painting if/or when the varnish is removed by separating the pigmented area of the painting from the solvents used in removal.
2. To seal any absorbent areas in order to create an even surface on which to apply the varnish.

CONSIDERATIONS AND CAUTIONS

To Apply or Not to Apply

An isolation coat can be very beneficial to the preservation of a piece of artwork but it is not for every painting. The decision of applying an isolation coat is first an aesthetic decision: Will this serve the purpose of the work? Secondly, are the changes created by the application of an isolation coat and subsequent varnish understood and anticipated? These are important questions to consider as the isolation coat will become a permanent part of the painting. Some ways that an isolation coat may negatively affect the underlying painting are:

• Foam and bubbles resulting from mixing Soft Gel (Gloss) and water too vigorously.
• Brushstroke texture
• Change and/or loss of texture
• Change or shift of color

Testing and practice should always be done before application to insure that the isolation coat will not change or damage the piece in any way that is undesirable. Here are a couple of examples of pieces that should not receive an isolation coat:

• Oil paintings
• Any painting done with water soluble media
• A piece with intentional varying sheens and surface qualities
• Work with metallic leaf (imitation gold leaf can tarnish with exposure to gels and paints)

To Brush or Spray?

In addition to the examples above, one must consider the application of the isolation coat. Since this is a clear layer, careful consideration should be paid to the brushstrokes within the painting as to not detract from them with the brushstrokes of the isolation coat. If the piece consists of poured films then a brushed isolation coat may cause distraction and spraying or avoiding an isolation coat may be the solution. Applying an isolation coat with a brush on a painting with a considerable amount of texture can generate foam. This may warrant a spray application or the decision to avoid an isolation coat all together. In the case of paintings that involve washes or stains of color, an isolation coat may be very important as the pigments may not be contained within an adequate amount of binder and could be underbound, making these areas delicate and sometimes too fragile for a varnish removal without the possibility of paint lifting. This may also indicate that a spray application of an isolation coat may be necessary to avoid any bleeding or smearing of the paints.

SEALING THE SURFACE FOR VARNISH APPLICATION

Sealing absorbent surfaces of the painting with an isolation coat will assist in the varnish application. This will prevent the varnish from being absorbed within the surface and allow the varnish to function as an easily removable topcoat. This is especially important when using a Satin or Matte varnish because the liquid of the varnish can be absorbed into non-sealed areas leaving the matting solids exposed at the surface and creating a dusty or cloudy appearance. To determine if you have a substantial isolation coat, once the first isolation coat is dry, look at the painting at an angle and the presence of an even sheen should indicate an even surface ready for varnish.

RECIPES AND APPLICATION

It is important to use gloss products