Making your own paints - Grinding pigments
Sometimes, you need to get have a special paint.


Many pigments are toxic to some degree - either in low doses over a long time or in higher doses in a single instance (cronic and acute poisoning respectively) - so, it is important for your own safety and that of those around you to adopt certain practices that will preclude such events.

To contaminate yourself with pigments (or other painting-related compounds), there are a number of routes into your body. The most obvious of these is your mouth. Others include your lungs, skin, nose, eyes and so on. Avoiding activities that allow things to come into contact with these routes is the most effective way of avoiding contamination. So, when painting or preparing pigments, paint, solvent:

  • Do not smoke. Apart from the obvious fire hazard with organic solvents, you will be putting things in your mouth that you have handled with your fingers;
  • Do not eat or drink for the same reasons;
  • Keep your painting related activities in an area that is away from your normal living area (you will be less vigilant when not painting so more likely to become contaminated);
  • Keep away from pets, partners and children, whether the materials are in current use or not;
  • Pigments are powders that you can breathe in so keep the dust level down by prevention - when mixing pigments, do things slowly and using as little force as possible thereby reducing the energy that can throw powder into the air.
  • Do not paint when intoxicated - you will not be as aware of the potential dangers;
  • Wear protective clothing so that your everyday clothes do not become contaminated - an apron will do, just something that is going to stop whatever it is that you are working with coming into contact with you or your clothes;
  • If you become aware that you might be breathing in more solvent than is healthy, increase the level of ventilation (if you are gilding, don't do it where there are solvents anyway as you cannot have drafts with such an activity.
  • Finally, clean up after you have finished. You don't want pigments mixing together but more importantly, you don't want to pick up any contamination from stuff that has not been cleaned away which you can then ingest by accident.

The above is not an exhaistive list. Feel free to be even safer in areas that are not mentioned above as well as those that are.

Grinding pigments

Copyright (c)2019 Paul Alan GrosseIf you buy pigments then many of them will already be very fine and really, all you will be using the muller and slab for is mixing them with the medium. However, if you make your own pigments or get pigments that do need grinding finer, you will need a surface that can handle them. On the right are the two surfaces that I use to grind pigments - Marble and Granite. You can also get glass with a ground surface.

Granite is nice and hard so the pigments are less likely to scratch it but if you can't get hold of granite, what can you get away with?

Okay with...
Granite   7
Glass plate   5.5
Lapis lazuli5-5.5NoOkayOkay
Marble   3-5
Lead White3-3.5MaybeOkayOkay
Egyptian Blue1-2OkayOkayOkay
This is a table comparing various materials that your slab can be made from compared to a number of different pigments that you might want to grind. You can see that most of them are fairly soft so a marble slab will do but there is nothing quite like grinding smalt on a marble slab to act as an incentive to find a granite slab.

*Note: Alum is a commonly used substrate that is used to precipitate dyes. This process is necessary because if the dye was not fixed like this it would migrate throughout the medium and not only would it dye other layers in the painting but if dye migrated through an opaque layer such as the painting's ground, you would lose sight of it.

Pigments that are dyes precipitated onto alum include: Indigo/Woad; Alizarin; Rose Madder; Madder Lake and so on. These have a 'gritty' feel to them when you start grinding them but being so soft, it soon smooths out.

Marble slab for grinding paint on. Copyright (c)2019 Paul Alan GrosseThis is marble. It is quite pretty to look at but you can see from the table above that it is actually quite soft. This is because it is formed by heating up chalk until it just about melts therefore it has the same sort of hardness as chalk.

If you do start grinding something that is harder than the slab, you will actually be grinding the surface of the slab away and that is what you will end up with in your paint. Smalt provides an excellent example of the damage you can do to a slab by grinding something that is too hard.

Purchasing a glass slab with a ground surface seems to be a particularly difficult thing to do at a reasonable price. I have seen suggestions that you buy a thick (6mm+) piece of glass and then use some carborundum and your muller to grind the surfaceof the glass but that means that you are also grinding away your muller and they are not cheap. A glass slab has a hardness of around 5.5.

Copyright (c)2019 Paul Alan GrosseThis is granite. It was on sale in a city centre shop as marble (so much for the knowledge of the shop's supplier - it was one of many and there were no marble ones so it was not as though someone in the shop had put the wrong label on it or something).

You can see that it is made up from a load of different crystals that have all set together in a single piece and the result of all of these harder minerals is that the resultant rock has a hardness of around 7.

On that, you can grind just about anything you are likely to want to use as a pigment. Even lapis lazuli has a hardness of 5-5.5.

I have ground smalt on a granite slab and it still takes some of the surface away but remember that granite is not a single mineral and there are likely to be softer minerals in it in the interstices of the crystalline structure.

Rubberised mat to put the grinding slab on. Copyright (c)2019 Paul Alan GrosseThis is a rubberised mat. You will need something like this to stop the slab from moving around on your work surface. If you can't keep the slab from moving, there is a danger that a piece of grit will get under it and start scratching your work surface. Also, if you are grinding your pigments for some time, having the slab move around is just wasting your energy and you will find grinding more tiring than it needs to be.

You can pick these mats up fairly easily and they don't cost very much. Your local supermarket or hardware store is your best bet - I'm sure the art shops would like to sell you something at many times the price.

Two different types of muller. Copyright (c)2019 Paul Alan GrosseHere are two different types of muller - the hand-held glass grinder that you will use for grinding your pigments down. They are not cheap but they will last you a long time if you look after them.

The muller with the short handle. Copyright (c)2019 Paul Alan GrosseThis is the muller with the short handle and how you would hold it. You can see that as you move it in a circular motion, the only things that are keeping it in your hand are the ends of your fingers and your thumb. Nothing else. If you have something that takes a lot of grinding, your fingers will get tired earlier in the process with this design.

The muller with the longer handle. Copyright (c)2019 Paul Alan GrosseThis muller has a longer handle that fits nicely in your hand and you can push with the heal of your hand and pull with all of your fingers together at the same time. This makes it a lot easier to grind pigments than the shorter of the two.

Circular motion you should use to grind paint. Copyright (c)2019 Paul Alan GrosseJust before we get onto individual types of paint, there is still one thing in common with water colours and oils and that is the motion you use to grind them.

If you have paint that you are mixing on the flat slab and you are pressing down with a flat surface such as the underside of the muller, the natural thing for it to do is to spread out and the more you chase it, the more it goes everywhere.

However, there is a way that you can move the muller that keeps pulling the paint back towards the centre of the slab.

If you are right handed and move the muller anticlockwise with an overall circular anticlockwise motion, as shown in the diagram with the purple line, the front edge of the muller picks up paint and drags it towards the centre of the red circle. If you are left handed, do it the opposite way around.

You will still need to use the palette knife every now and then to scrape the paint of the rim of the muller but you shouldn't need to be using it all of the time to collect it from all over the slab until you have finished.

All images and original artwork Copyright ©2019 Paul Alan Grosse.