Glass Mullers
~for mixing and grinding paint and varnish pigment

Functional Simplicity - The Muller is a beautifully hand made object of solid borosilicate glass. Grinding is done in the traditional way by hand, on a hard slab surface of glass or stone. The base of the Muller is ground with a fine tooth surface that is ideal for grinding pigment. It has a slight convex curve which allows pigment to become forced between the wedge of the working surfaces.   "Beautiful high quality muller! Great service, thanks!" ~Thrasyllus

"Great little muller; perfectly described, nicely made, just love it and very nice to deal with." ~Redding Canvas The Glass Muller is used for grinding pigment and dispersing the pigment into an oil or water base. It is used on an even grinding surface such as glass or marble. The Muller is designed to mix paint pigments thoroughly with whatever base the artist chooses to use and enables the artist to grind pigments to the color and consistency of their choice. The glass I use for making the muller is medical grade borosilicate Pyrex® glass, autoclave safe, non-porous, and 100% lead-free, the same as I use for body decoration. You can read more about the borosilicate glass I use by clicking here. "A beautiful piece of art ! to create art ! Thank you!" ~1959gal

The working face is approximately 50mm diameter and the muller has a bulbous handle that is specially formed to provide a comfortable grip. The handle can be colour-coded for ease of use. This is to enable stained glass artists (in particular) to identify the muller they use for stains, otherwise the stain will contaminate and spoil other colour mixes.

Please note that this item is supplied with a clear handle unless a particular colour is requested. At an extra cost of $10, I can colour the handle to your requirement; opaque and translucent colours are available.

Extra Heavy Glass Muller, 50mm diameter: $38

P&P: $8

Tip of the day; check out these suppliers; Sinopia & Kremer ($52 + $11.50shpping) and Art Boards™ ($65) for a sobering and startling comparison to my prices.

There may be a slight variation in shape and size as mullers are hand made by me, in my studio.

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A word about using a muller and grinding

Mullers are used by all artist needing to grind their own pigments including fresco painters, stain glass painters, oil painters, tempera painters and more. It is the perfect addition to your artist’s tool kit.

Use the muller on a slab of marble or granite (ideally porphyry) or a thick sheet of glass to grind and disperse pigments and other materials into paint medium. Both surfaces of the muller and the grinding slab can be retextured periodically after use with a slurry of water and 100 grit silicon carbide although 80-grit carborundum paper is sufficient for most users.

To disperse pigments in paint medium, place a small quantity of powdered pigment on the grinding surface and work in oil or water a little at a time with a spatula until a stiff paste is formed. Begin grinding the paste in circular or figure 8 motions until the paste has a smooth consistency. It is not necessary to bear down with your weight on the muller since the idea here is to disperse, rather than to grind the pigment.

Some artists insist that a heavy, six-inch muller can only be effective. I fully understand that it is good to use a technique you are used to however, it is also good to be aware of other techniques :-)

Hence I use a small muler, which is quite adequate I find. Although a ten pound weight pressing down on a six inch diameter muller equates to 0.4 pounds per square inch, the same ten pounds pressure applied to a one and a half inch muller equals 5.6 pounds per square inch.

Also consider the wastage of paint lost in cleaning a big muller. The glass plate that I mix paint on for stained glass painting is only eight inches square, that's all I need.

I think it may also be worth mentioning that one of the greatest assets to mulling paint, is the surface tension of the muller in the actual pigment. If it is kept perfectly square and flat during the mulling proccess, the force that is acquired by surface tension alone, is enough to offset using a small as opposed to a large muller. It does need practice as I found.

Getting the heaviest muller possible isn't necessary; keep in mind that while grinding the aim is to achieve a shearing force, which requires lateral movement rather than downward pressure. Use your strength to grind across the grinding surface rather than applying downward force.

Get in the practice of using a hard rubber or plastic spatula to scrape the surface and collect the paint into a pile. The iron in steel spatulas may react with certain pigments, such as sulfide pigments. You can always use a steel spatula for clean up.

Grinding Colors and Making Oil Paint

Ultramarine Blue

Ultramarine blue pigment is one of the more difficult pigments to disperse in oil when trying to obtain a paste or buttery consistency. It gets either stringy, long or fluid in consistency. When adding oil to a small pile of the pigment on a grinding surface, at first it may not wet easily, then suddenly it becomes soft and fluid. I have found that if you have ultramarine color in this state, put it aside for a week in a closed can or wide mouth jar. Then bring it our once again and grind it further, adding a little more pigment to the mixture, if necessary, to develop a thick paste.

Genuine Vermilion and Cinnabar

The problem encountered when dispersing heavy inorganic pigments, such as vermilion, is separation from binder. To prevent this some manufacturers would add beeswax or stearates to the oil.

Cadmium Yellow

The proportions of mixing and grinding medium cadmium yellow in oil should be 74 percent by weight of dry pigment and 26 percent by weight of refined linseed oil. When using raw linseed oil, and under certain conditions, as, for instance, in the case of a very bulky yellow (it appears very fluffy), 30 percent of oil and 70 percent of pigment will produce a paste. Poppy seed or walnut oil may be substituted for linseed oil. In all cases, be sure and grind this mixture well to prevent separation while it is stored in the tube. It would not be too lengthy to grind this mixture continuously for an hour with a muller.

When you to want to make an "extended" cadmium yellow, 40 percent oil should still produce a paste that when thinned will provide good covering power. The extending material for cadmium yellow is principally barytes, although calcium carbonate (whiting or chalk), terra alba or bentonite may be used. A good formula for extending medium cadmium yellow to achieve a lighter tone is 30 percent by weight of medium cadmium yellow, 45 percent of blanc fixe and 25 percent of refined linseed oil.

Grinding Ultramarine Blue

Native ultramarine blue, or lazurite (also known as lapis lazuli), many times lacks the brilliancy of the best artificial grades available today. We have found an exception to this rule in the premium lazurite from Chile offered by Natural Pigments.

In oil, native ultramarine or lazurite is more transparent, while the artificial pigment is more opaque and greater tinting power. The reason for this is that the native pigment typically contains calcite, which is transparent in oil. The native pigment can also be granular in texture and somewhat refractory in grinding. Natural Pigments lazurite from Chile is very pure and has the highest tinting strength of any native lapis lazuli. The average particle size of the native Chilean blue from Natural Pigments is 20 microns. While this is larger than the artificial product, which can be less than 5 microns, any smaller granularity in the native pigment would loose the unique quality of the native pigment, this quality being impurities, such as pyrite, which can glitter like stars in the paint.

To grind native ultramarine in oil it will be found that 60 percent by weight of oil to 40 percent of pigment is a good average to figure on, but as the specific gravity varies considerably these figures cannot to be relied upon as an absolute. For Natural Pigments lazurite from Chile, use 65 percent by weight of pigment to 35 percent of oil as a good starting point.

There is an incredible variety of artificial ultramarine blues on the market today and available in a large number of grades. There are two distinctive processes of preparing this pigment, one being known as sulfate ultramarine, the other as soda ultramarine, the latter having a violet undertone, the former leaning to a greenish tint. In either process, the constituents are nearly similar, comprising kaolin, sodium sulfate, sodium carbonate, sulfur, carbon, quartz and infusorial earth. Not all of these are used in one operation, if, for instance, quartz is used infusorial earth is omitted and vice versa.

Sulfate ultramarine blue may be recognized by its having a slightly greenish-blue undertone when ground in oil, while soda ultramarine blue has a violet-blue character. The better grades of soda ultramarine blue are preferred for tinting whites, because the whites are not so apt to become greenish.

For grinding ultramarine blue in oil, the one that has the strongest tinting power should be selected and the average mixing will require 67 percent by weight of pigment to 33 percent by weight of linseed oil. This ratio of pigment to oil is only a starting point, because each grade of ultramarine blue and the type of oil used will vary the amount of oil absorbed. Refined linseed oil is preferable to raw or boiled oil, as it will give the blue a clearer tone and appearance.

For an exceptional clear appearance and to prevent any greenish cast in the oil color, use refined walnut oil or poppy seed oil. Separation of oil and pigment can be avoided if the blue is ground in a mixture of 75 parts refined walnut oil or poppy seed oil and 25 parts of heat-bodied oil or stand oil, which will aid the drying time of the color; 65 parts by weight of ultramarine blue to 35 parts by weight of the oil mixture will be about the right proportion.

As noted above, ultramarine blue pigment is one of the more difficult pigments to disperse in oil when trying to obtain a paste or buttery consistency. It can become stringy or "long" or very fluid in consistency. When adding oil to a pile of the powder pigment on a grinding surface, at first it may not wet easily, forming a crumbly mass, then suddenly become soft and fluid. We have found that if you have ultramarine color in this state, put it aside for a week in a closed can or wide mouth jar. Then bring it our again and grind it further, adding a little more pigment to the mixture, if needed, to develop a thicker paste.

Genuine Vermilion and Cinnabar

For artists' grade color, use the best grade of vermilion known as Chinese, or high quality native cinnabar, both of these pigments are available from Natural Pigments. Vermilion is the name of the artificial pigment, while cinnabar is the designation of the native mineral, both of which are chemically red mercuric sulfide (II).

To grind vermilion or cinnabar, 86 parts by weight of the dry pigment to 14 parts by weight of linseed oil, walnut oil or poppy seed oil is about the right proportion for mixing. Due to the heavy specific gravity, the pigment separates from the oil in tubes and some have resorted to using wax with the oil to keep pigment and oil together in storage, and while this can be employed successfully, you may have trouble with the color on account of the presence of the wax. The drying of oil can be seriously impaired by wax. Stearates are also effective in preventing separation. A better and safer plan is to grind the pigment in part linseed oil, walnut oil or poppy seed oil and part heat-bodied linseed oil, such as is used in making lithographers' ink. The proportion of the two oils varies considerably depending upon the viscosity of the heat-bodied linseed oil. You can later thin this color with gum turpentine for easier brushing without impairing the gloss or life of the color.

Using Additives

Generally, there is little need for additives, such as aluminum hydroxide or wax, unless you want to adjust the rheological properties of paint. Let me explain: What you are essentially doing when mixing powdered pigment with binder is punching many tiny holes into the fluid and then displacing some of the fluid with the pigment. A second operation is breaking up agglomerates and aggregates of pigment particles into discrete or basic particles. This requires an amazing amount of shear force to accomplish and this is precisely what the muller does on the grinding slab. It applies shear or tearing force to the pigment particles and vehicle in order to achieve a homogeneous mixture.

There is a third problem when it comes to dispersing pigments: overcoming the surface energy of particles. The greatest contribution to viscosity of any dispersion is due to the particular nature of the pigment. Particle size is also an important contributing factor. The smaller the particle size the more surface area and hence more energy to overcome in order to wet pigment particles. Conversely, the larger the particle size, the lower the surface area and the surface energy, and easier it is to wet. It is also less likely for larger primary particles to form new agglomerates. Consequently, larger particle-sized pigments exhibit lower viscosity and increased flow relative to their small particle-sized counterparts.

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