Pigment Grinder

Pigment Grinding, I am looking for sources in Canada to grind scale, I have been collaborating on a project with a Metal Smith. We are making BW prints using scale from his forge, I would like to grind it into a finer form so when its laid down with exposure its not so gritty (looks cool) but we want to push this envelope a bit further. Any sources for grinding or suggestions on machines to purchase that do not break the bank would be appreciated.

I think that the tool you are looking for is a ball mill. These devices are sort of like industrial rock tumblers, except instead of using polishing grit, one uses steel or ceramic balls.

I'm guessing that scale from a smith's forge is iron oxide, which I imagine is not particularly hard. And, I imagine you are not wanting to grind large amounts of material. Thus, you might even get away using a hobbyist rock tumbler for small batches. You'd use balls instead of 'grit' as mentioned above.

I'm sure that an industrial mill would last longer than a rock tumbler, but the tumbler is likely to cost much less.

fgorga said:

I think that the tool you are looking for is a ball mill.

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Yep. They range from sub-$100 to multi-$k. Mine is in the former category and is just fine for dispersing pigments, but I doubt it would do much good at grinding them. It's one thing I'd still like to try one day.

Apart from the mill, what matters is the milling media and the vessel. That's about as far as my knowledge stretches. I'm using plain stainless steel shot in mine and the vessel on my cheap mill is a rubber affair I would trust about as far as I could throw it (it helps it's pretty light!) When processing small batches of a few grams of pigment, I put the pigment with the dispersant and some water and some steel shot in a plastic 35mm box and then put that in the larger milling vessel. Works very nicely.

fgorga said:

I'm guessing that scale from a smith's forge is iron oxide

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If it is, it's a b*tch to print with in my experience. It's virtually impossible to disperse effectively so it'll always settle to the bottle. And since it's a ferromagnetic material, it'll orient itself in the direction of any nearby magnets, so forget about trying to keep it dispersed by putting it on a magnetic stirrer.

@Carnie Bob I know Calvin has mentioned his planetary ball mill a couple of times; he seems to have looked into the matter and since he also does work with natural pigments, I guess he must have looked into the issue of grinding to a homogenous size as well. Have you contacted him about it?

My brother experimented with mixing up his own artists oil paints. He used a thing called a MULLER.
Basically a 5" diameter glass disc, about 1" thick with an integral handle similar to a file handle on top.
The whole thing is one glass moulding.
The material to be ground is placed on a piece of plate glass and the flat face of the muller pressed down then moved in a rotary fashion. The pigment was ground in this way until the right consistency.
Some of the pigments he ground were quite hard in the first place so it may work for for scale.



Google artists glass muller for more information.

BobUK said:

My brother experimented with mixing up his own artists oil paints. He used a thing called a MULLER.

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These are OK_-ish) for dispersing pigments in order to make, for instance, paints. They're not appropriate for grinding pigments. There's an unfortunate mix-up of terminology in the art world where people who make paint speak of 'grinding pigment', while in fact very little to no grinding takes place. Btw, I use a paint muller from time to time to make really small batches to test with colors/pigments etc. or to make a dispersion that doesn't have to be very accurate/precise in terms of pigment load.

The dispersion quality you get with a muller is abominable when compared to even the cheapest ball mill.

A crude tool for grinding pigments is a mortar & pestle, but it's no good at getting the fine particle size needed for decent printing, nor is it any good at achieving a uniform particle size.

Some kind of mill is really the way to go.

Thanks koraks, I never realised the true purpose of the muller.

Geologists use sieves to grade material. You have most probably seen them. Ranging from fine powders to golf ball size.

Very expensive new, but can sometimes be seen in good condition second hand at reasonable prices.

The maker that springs to mind is Endecotts.

BobUK said:

Geologists use sieves to grade material.

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Sieving is certainly useful in this application to make the first selection between coarse muck and the base material to start grinding. From this point onwards, I doubt if sieves play much of a useful role. Keep in mind that a good printing pigment will have a particle size in the range of dozens up to a few micrometers at most.

Also, when grinding pigments, you typically do so in a wet state. After that, it's neigh impossible in a small-scale/non-industrial setting to dry them without them caking all up into a massive lump. You typically grind and disperse at the same time. So sieving as a means to select out the desired particle size from a heterogeneous mix seems like a non-starter to me, apart from the initial coarse sifting.

A mill is really the way to go.

I’ve had better luck using a muller on a thick glass slab with small batches—really helps crush the pigment evenly. Whole process takes time but worth it for consistency.

Welcome aboard @Hayrackba ! I've had some success with a muller, too - indeed, in small batches. But the best results I get with a tumbler. I have a simple rock tumbler and usually put a few grams of pigment into a 35mm film box together with some steel shot, some water and a dispersing agent. Then let'r roll for an hour or so. The result is a perfect dispersion, assuming that the pigment is fine and of even particle size to begin with, which is generally the case with commercially bought pigments. Natural (rock) pigments may need additional milling if they're procured in a raw form (which I wouldn't recommend). A muller isn't a very suitable tool for this as it would take many hours to effectively grind even a small batch of pigment.

Hayrackba said:

I’ve had better luck using a muller on a thick glass slab with small batches—really helps crush the pigment evenly. Whole process takes time but worth it for consistency.

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I’ve been using concrete oxide colours as dry pigments and grinding them with a simple Muller and glass plate. They’re super fine already, so it doesn’t take long to get a smooth mix. They work great if you're aiming for dense colour in gum prints or other alt processes. Just make sure to use a mask while mixing them dry—they’re really light and easy to inhale.

Dick Sullivan tells of when he needed a ball mill, so used a paint can and a motor base. He left it to rotate over night (might have a longer total time) and in the morning found that the steel balls had ground the end of the can off. Quite a mess.

Vaughn said:

so used a paint can and a motor base.

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Yeah, better try something slightly more solid. It doesn't have to be the fancy kind of planetary ball mill with zirconium pellets that Calvin Grier uses. Something as simple as this works fine in my experience: https://www.aliexpress.com/item/1005009347416649.html
Just use some steel shot for the milling. I put the pigment into a 35mm film box with the shot and then put that inside the actual cup.