As with any technique, if you've never tried this before it is advisable to practice on some cardboard or scrap material first. The process is fairly straight-forward, but requires some attention to the guidelines detailed below.
The first coat of paint laid down will be the colour that shows through as the cracks. This first coat should be a water-based paint such as Derivan Student or, for larger areas, Derivan Chalkboard paint will give the best results. Leave this coat to dry before going to step 2. It is possible to omit this coat. If the desired effect is to show the surface as cracks, the Cracking Medium can be applied directly to any surface that acrylic paints will normally adhere to. For example, if cracking on a wood surface and the desired effect is to have the paint cracking to reveal the woodgrain underneath, skip step 1 and start at step 2 ensuring the surface is clean and free of oil, grease and dust.
Once step 1 is dry, apply Derivan Cracking Medium (water-based). You can use a brush, sponge applicator or roller (either a sponge or short nap roller). Apply the Cracking Medium so that it is as thick as possible but not so thick that it runs when the surface is held vertically. The Cracking Medium is designed to be a high-build coat; therefore, it is very viscous (thick). Do not be overly concerned with obtaining an even flat surface as the Cracking Medium has a built-in flow agent which will allow it to level out as it dries.
It is possible to thin the Cracking Medium down with water so that it may be sprayed through a spray gun for larger areas. The amount of water used should not exceed 25%. Also keep in mind that the medium must be at least 1-2mm thick to work. Always do a test with the equipment to be used and the dilution rates before embarking on a large project.
Use approved respiratory equipment if using a spray gun, and do not inhale the Cracking Medium.
This is the coat that cracks to reveal the coat applied in Step 1. Step 3 must be applied within 12 hours of step 2 drying. The paint used MUST be Derivan Chalk Board Paint or Derivan Student Paint as the Cracking Medium has been especially formulated to work with this paint. The special formulation, unlike some other brands, allows for different types of cracks to be achieved and repeated with consistency. The Matisse Flow or Structure ranges will not always work as a topcoat with the Cracking Medium unless they are mixed with MM5 Matt Medium (this is discussed further in Cracking Metallic and Tube Colours).
When applying the topcoat, it is important not to re-work areas that have already been covered as re-working an area can lift the cracking coat and stop the process (see below for more details).
How it works
The old methods of cracking using gum arabic and forced drying were quite unreliable. They relied on the different drying speeds to crack the paint. The climate had to be just right and the slightest mistake would result in the process not working.
The Matisse cracking process relies on a reaction between the topcoat of Derivan Chalkboard paint and the Cracking Medium which has been applied below it. Once the topcoat is applied, the cracking coat below becomes semi-liquid again and shrinks, taking with it the topcoat.
It is worth noting that the topcoat should be applied systematically, covering the surface and not going over an area that has already been covered. As described before, the paints have been designed not to crack; therefore, when the Cracking Medium is trying to shrink and take the topcoat with it, the topcoat is actually trying not to break apart.
The thickness of the topcoat will dictate how big the cracks are. The thicker the topcoat the more easily it is able to hold together and resist cracking but when the Cracking Medium gets its way and manages to crack the topcoat, it will result in a very large crack. Thus the thicker the topcoat of Matisse Background Colour, the fewer the cracks but they will be big ones.
Conversely, if the topcoat is applied very thinly, the Cracking Medium will encounter less resistance from it and therefore result in many more cracks but they will be much smaller in size.
How to achieve different patterns
Following on from above, it can be seen that if the topcoat were to be applied using a brush and brushing in the one direction, the overall pattern of cracks would be in the direction of the brushstrokes. This is because even though one aims, when using a brush, to lay down a nice flat coat, in reality if the brushstroke is studied closely, the topography of the paint has corrugations in it. These corrugations run parallel to the drag of the brush.
As described above, the paint will tend to crack at its least point of resistance or where the paint is the thinnest. Therefore the thinnest parts in a brushstroke are the troughs in the corrugations, which in turn give the elongated cracking pattern.
If a sea sponge is used to apply the topcoat, the topography becomes more akin to sand dunes; therefore, the resultant pattern would be more rounded and random.
Other influences on patterns
The types of cracks obtained depend on the thickness of the topcoat and the way in which it is applied. The bottom coat has no bearing on the outcome of the cracking pattern. The way in which the cracking coat is applied will not affect the pattern, unless it is too thin, in which case it just won't work.
The surface on which the finish is to be applied may have some bearing on the pattern. For instance, if very large cracks are desired, the topcoat will need to be applied very thickly. It will be necessary to have the surface horizontal as the weight of the paint may run and pull the cracking medium if the surface is vertical.
On frame mouldings or 3-dimensional pieces the paint, as it cracks, will tend to sink to the lower surface due to gravity. This may leave edges or sharp points exposed and make the piece look contrived.
If the artist is new to this finish, it would be prudent to do some tests on an old sheet of cardboard etc. before a large project is attempted.
It is not necessary to varnish the cracking finish unless it is to be used on utility items with a lot of wear and tear or if it is to reside outdoors.
The cracking medium may also give a higher sheen to the first coat (i.e. the cracks) than the topcoat. A varnish may be used to even out the different sheen levels as well as protecting the finish from water and some wear and tear.