Aluminium Composite Panel
The opportunity to paint watercolor on a giant scale without the need for glass, opens up all sorts of possibilities. In this article we will look at preparing and using a large panel to accept watercolor.
Watercolor has traditionally been a small scale painting medium, generally limited by the size of a standard sheet of watercolor paper (22×30 inches). Protecting finished watercolors with glass also places a limit on size. Once a sheet of glass gets beyond the size of a full sheet of watercolor paper, the work becomes heavy and breakage due to twisting becomes a problem.
One of the best ways I have found to overcome the limitations of size is to use an aluminium composite panel primed with watercolor gesso then, after the painting is completed, protected with a finishing varnish.
Aluminium composite panel is a thin, rigid sheet made from a polypropylene core sandwiched between two thin sheets of aluminium. It is stable and robust and will not absorb moisture like organic surfaces.
Aluminium composite panel is available through many building and sign writing suppliers. A search online will find suppliers in your area. If you have difficulty finding it, try your local sign company. They will often have off cuts.
Cutting Aluminium Composite Panel
The first step is to cut the composite panel to the size we want to work on. The easiest way is to have the supplier do this. I usually have the panels delivered in 6×4 foot sheets. These can then be cut down by repeated strokes with a sharp craft knife along a straight edge. This gives a nice straight cut but takes time and effort. A jigsaw makes the job easier, but the cut is not as neat.
Sanding Aluminium Composite Panel
To prepare the panel for gesso, roughen the surface with a medium grit sandpaper. The panels can be ordered with a primer finish or simply matte or gloss white. Primer finish is best but, if you are buying off cuts, any white or very pale finish will be suitable.
A thorough light sanding will provide a good tooth for the first coat of gesso.
Priming Aluminium Composite Panel
After the panel is evenly sanded, wipe it down with a damp cloth. Two coats of regular gesso will bond to the surface and make a clean white undercoat. Once the regular gesso is dry apply three coats of watercolor gesso.
Allow plenty of drying time between coats – each coat must be completely dry before the next is applied.
There are a number of watercolor gessos on the market. I like the Golden Paints absorbent ground. It makes a great absorbent surface, but contains little pigment so the undercoat of regular gesso is important.
If you prefer a smoother surface, sand lightly between coats and thin the gesso slightly with water.
Once the panel is thoroughly coated allow it to dry for a couple of days before painting on it.
The color swatch on the left was painted onto regular gesso. The beading shows how the surface rejects the pigment.
The swatch on the right was painted onto Golden Absorbent Ground. The pigment absorbs evenly into the surface with no sign of beading.
You will have to make a slight adjustment to the way you paint. Pigment tends to sit more on the surface like a heavily sized paper, so vigorously working over painted areas will lift off underlying layers. The secret is to be gentle and wait for things to dry.
Lifting back into previously painted areas is easier than on paper and areas can be completely reclaimed with a couple of coats of gesso.
The ease of lifting off pigment influences the way you paint – lightening tones, softening edges and removing areas completely quickly become part of your painting technique on these surfaces. The detail of rocks above shows how applying a darker than needed tone then washing the pigment back produces interesting graduations and textures.
The absorbent nature of the watercolor gesso makes for a soft surface so a protective varnish must be applied to the finished work. Best protection comes from acrylic varnish. Either mat, satin or gloss depending on your preference. I use a light spray of workable fixative on any charcoal or pastel marks prior to spraying with acrylic varnish.
Acrylic varnish can be sprayed on with a compressor driven spray gun. I lay the work flat then walk around it spraying from all sides, pausing every few minutes to allow the varnish to dry. I like to build up 5-6 thin coats this way.
The other method of application is by brush. A wide, fine bristled nylon brush works best. They don’t shed bristles and leave very few brush marks.
Evenly apply the varnish with a minimum amount of brush strokes. You want to avoid making the varnish lather, trapping air bubbles. The varnish will appear milky when first applied but this disappears once it dries. When applying by brush three even coats are usually enough to get a smooth, even coverage. Make sure your painting is thoroughly dry (leave at least 2 days) before varnishing with a brush.
An eerie stillness along the Dunedin Waterfront. Big graded watercolor washes were built up in layers through the sky and foreground, each wash drying thoroughly before the next was applied. The detailed buildings are a mixture of watercolor, gouache, charcoal and ink. To exaggerate the light in the sky, a patch of white gesso was feathered over the initial washes.
Pale washes of watercolor built up the foreground and distance in this painting. A band of dark trees and detail around the buildings were added before vigorous strokes of gesso were worked into the sky with a 2 inch brush. This area of light was then softened around the edges with a dry hake brush.
If working larger appeals to you, or you would just like to do away with glass, visit your local sign writer and try out this great material. All the fun of watercolor without the limitations!
Author: John Lovett