Muller and slab (or pestle and mortar)
Small pots to store paints
Pigments are coloured powders made from chemical compounds that do not dissolve in water. Sandby would have bought most of his pigments from the greengrocer or apothecary, but today they are available in specialist art shops. Pigments need to be ground very finely to avoid gritty paint.
Gum arabic is made from the solidified sap of the thorny acacia tree. When pigments are mulled with gum arabic solution (1 part gum arabic to 2 parts water) their tiny particles become suspended in the thick, sticky liquid, which can be applied to paper using a brush. The gum also fixes the pigment particles to the paper surface.
Glycerine (optional) can be added to prevent the gum arabic from chipping or cracking as it dries. It can also help the gum arabic to re-dissolve more easily in water. This can help artists to repaint areas on the paper once they have already dried.
Honey water (1 part honey, 1 part water) can help stop the paints from drying out. Honey is very good at retaining moisture, but if too large a quantity is used paint can go sticky!
Mix 1 part of honey water with 2–3 parts gum arabic solution. Add a couple of drops of glycerine. Sandby often added a couple of drops of alcohol to break surface tension, but do not do this unless you are 18 or above.
Put a level dessert spoon of pigment onto the mixing slab and make a small hole in the middle of the powder. Drop enough of the solution in to just fill the hole.
Grind the ingredients together using the muller. This is best done standing up, moving the muller in a figure of 8 motion. The friction of the muller will make the water evaporate as you go. Periodically scrape the paste back into the middle of the slab.
The ingredients will eventually amalgamate to form a thick, creamy paste. Scrape up the watercolour with the palette knife and press into a suitable container.
It may take a couple of attempts to produce the perfect paint. Finding the right strength binder for a pigment can be a process of trial and error so patience is required.
Reference: 'Sandby's Materials and Methods' talk on 26 August 2009 at Nottingham Castle Museum and Art Gallery