Home-made Lead Carbonate

 

 

To follow up on the preceding article: I have discovered that making your own lead pigment the old-fashioned way is far, far easier than I thought.

Dutch, or stack process white, whatever you want to call it, was generally made by putting pots containing lead and vinegar into a shed full of horse manure, or at least buried in a large pile of it. The vinegar fumes corroded the metal to make lead acetate, which in turn was converted to lead carbonate by the CO2 and water vapour released by the rotting manure over several months. I got the idea somewhere that you needed a very large minimum volume of manure in order for the decomposition to produce enough heat. I was wrong.

I found these two painters on the internet, Luis Borrero and Zachary Kator, both explaining how to do it on a small scale:
                http://paintingperceptions.com/sounding-technical/the-great-lead- white-shortage
                http://zacharykator.blogspot.ca/2010/07/about-lead-white.html

I'm hugely indebted to both of them. I can now make paint of incredibly high quality, for cheaper than any mediocre stuff that comes from the store. If and when lead pigment or even lead paint is banned or becomes economically unfeasible, I'll always be able to make my own, as long as sheet lead, horse manure and vinegar remain available and unregulated.

So here is my own procedure, which is a bit more precise and controlled than those above. It makes up to 6 lb of lead white in one go...

 

How to Make Lead White Pigment

Before you start, you need to have a good understanding of what is and isn't dangerous about lead. Don't be afraid of it, but don't get casual about it either.

Lead compounds are toxic, and if you're the sort of mucky pup who gets mysterious smears on your clothes and chocolate fingerprints all over everything, you probably shouldn't be trying this. But if you're generally aware of your surroundings and capable of being tidy, you'll be fine just by understanding the risks and using common sense.

Lead pigment in any form is dangerous if it gets into your mouth, and when powdered is especially dangerous if you inhale it. But it's not easily absorbed through the skin, which is why Titian lived so long in spite of finger painting with lead paint. It's significantly more dangerous to small animals and children than it is to adults.

When there is any dry pigment around, wear a proper respirator, with lead/asbestos cartridges. Make sure you don't disturb it in a way which makes floating dust... if it gets on the floor you'll track it around everywhere. Also, be careful of pigment in water that dries out, slopped on a counter top for example, or on the side of a jar. Always be conscious of what you might have contaminated. Don't get it on your clothes, and wash your hands thoroughly after handling it.

So...

You will need:
                -A large plastic storage tub
                -Some fairly fresh horse manure
                -Cedar bark mulch, the kind that's shredded
                -A plastic sheet of some kind
                -6 very large plastic or glass jars or vessels (with lids if possible), to be specified below
                -A jug of white vinegar
                -A sheet of 1/16" thick lead
                -An old knife or anything to cut the lead with
                -Some kind of protective rubber gloves
                -A fairly clean rag
                -Acetone

                -A medium sized plastic bucket
                -Various large jars
                -A Pyrex baking dish
                -A hotplate

 

Step 1:

Get some 1/16" thick sheet lead. Try looking under "lead" or "metal" in the yellow pages.

Measure and cut 6 lead strips 3" wide by 24" long. Each strip will weigh almost exactly 1 lb and will yield about the same weight of lead pigment. Give them all a thorough going over with the rag and acetone to remove any grease or filth or whatever. Carefully bend each strip into a coil roughly 3 1/2" wide.



Lead coils

 

Step 2:

Find 6 large, non-reactive jars or vessels of some kind which are plastic or glass, and can hold liquid in the bottom. Each should be large enough to enclose one of the above coils completely, with room to spare around the sides, though open at the top. In my experience, enclosing the coil around the sides produces the cleanest reaction, while for some reason, a coil sticking out of a shorter vessel is liable to develop a bit of brown discolouration. I use old plastic Hellman's large mayonnaise jars, which are the perfect size, about 4 1/2" wide by about 7" tall. But they changed the design, so you'll probably have to use something else.

Rig up a non-reactive support of some kind in the bottom of each jar, for the lead coil to sit on. Whatever you use, you want the coil to sit about 3" above the bottom of the jar without falling over, and without touching the vinegar which will later go in the bottom. Yet it must still be exposed to the rising fumes. One way of doing this is to stick two bamboo skewers through the jar (assuming it's plastic).

Another way is to find a plastic bottle 3" to 3 1/2" wide, cut a 3" section from it, and place a strip of wood or plastic on it to support the coil. It's probably unnecessary, but I cut big holes in the strip to let more fumes through.



A vessel

 

Step 3:

Get a plastic storage tub like the one in the pictures. It's roughly 18" x 18" x 22", about 25-30 gallons without the lid. Find a stable or somewhere you can fill it with horse manure; people with horses are generally desperate to get rid of the stuff. Allow them to be grateful to you for taking it away; the reality is you're not really helping at all, because the amount you need is infinitesimally small compared to that produced by even a few horses in a few days.

Ideally it should be as fresh as possible, but if some of it is a day or two old and dried out a little it will still work very well. Find a relatively clean surface, your driveway for example, and dump it into a pile. Separate it into three smaller piles, then make a fourth the same size of cedar bark mulch. Mix it all together thoroughly so it's about 25% cedar and 75% manure, then refill the tub about 2/3rds full. I've no idea whether the cedar is really useful or not; maybe it's to slow down the decomposition of the manure for some reason.

Add a little water to make sure the mixture in the tub is about as damp as a wrung out sponge. I used pond water just in case the chlorine in tap water would effect the decomposition, but this is probably completely paranoid. Put the tub outside some place where it can sit for several months, preferably in as much sun as possible. Ideally you should do this in the summer when it's hot; it may take more time in cooler weather.

 

Step 4:

Get the vessels and put about 10 fl.oz of vinegar in each. Then put in the lead coils. Cap up the vessels, so as not to get stuff in them while arranging them. Make little pits in the manure, and put them in, part way buried. Don't compact the manure too much.

Remove the lids from the jars. Put the plastic over the top of the tub, then put the lid on, putting a rock or something on top to prevent it blowing off in a high wind. The plastic probably does absolutely nothing; I'm just mindlessly copying what I saw someone else do for reasons I don't understand.



The vessels in place...


Sealed up

 



I also tried a round tub. For some reason it didn't work well
at all... it corroded unevenly and formed brown stuff on
the edges. The rectangular tub works much more reliably.

Step 5:

Leave it alone for 8-12 weeks. Actually, it wouldn't hurt to check it once a week, to make sure everything's all right, especially early on. The coils should start to turn distinctly white after just a few days. Don't worry when the manure starts to get moldy.

After 8 weeks they'll likely be entirely converted to white lead; after 12 weeks they certainly will be if you did it properly. What started as metallic lead will be puffed up into a fragile mass of flaky lead carbonate, like toxic white pastry.

The flakes should be beautifully white, ideally without any grey or brown, but don't be alarmed if you see bright turquoise discolourations forming on the edges. These are just copper compounds forming from impurities in the lead; they're highly water-soluble, and will come out later in the washing process.



After 8 weeks...


A fully corroded coil

 

Step 6:

Put a lid on a vessel, and remove from the manure. Clean off the outside, then dump most of the lead flakes into the bucket, then rinse the vessel with water to wash the remnants into the bucket as well. Wearing rubber gloves, mash up this soggy white mess as finely as you can, then transfer/rinse it into a large jar, maybe 30 fl.oz, with a good lid that seals well.

Let the water settle, then carefully pour off as much as you can without losing pigment. Then fill the jar with vinegar and cap it up. Leave it for a few weeks, stirring it every day. The vinegar will gradually dissolve the small flakes into a fine pigment. You may want to pour it off and replace it; for some reason it loses its effectiveness after a while.

 

Step 7:

When the pigment has dissolved as much as possible, pour off the vinegar and replace with water. Wipe the mouth of the jar to keep any pigment from preventing a good seal, and put the lid on. Shake it thoroughly, and let it settle. Repeat this washing process several times until it no longer smells of vinegar.

 

Step 8:

Swirl the contents of the jar, then pour 2/3rds of it into the Pyrex dish. Add more water to the jar, and repeat; in this way you can to some extent separate the finer pigment from the coarser remnants in the bottom. Collect this coarse stuff in another jar, and try dissolving it again in vinegar later.

Let the water in the Pyrex dish settle, then carefully pour off as much as possible. Put the dish on the hotplate to dry out. If you're worried about dust, put a piece of glass on top, propped up at an angle on scraps of 1x2 or something. It will cover the dish, but the water condensing on it will run down off the low edge, rather than dripping back into the lead white.

Leave it overnight. To make sure it's dry, watch for it to stop steaming, then give it a few hours more. The dry lead white will have big cracks running through it like dried mud.

Put on a respirator. Loosen the pigment from the bottom with a spatula or painting knife or something, then spoon it all into a 16 fl.oz jar. Don't worry that it's in caked lumps rather than a fine powder; it may even be easier to deal with that way.

 

* * *

 

You now have one pound of lead white, which you can grind with oil whenever you want, and of course, five more pounds waiting to be processed the same way.

Paint made with this pigment is different from any other, even home-ground lead white made with industrially produced pigment, which is really excellent. When you grind your own paint using industrial lead white and cold-pressed linseed oil, the oil absorption is very low. Using the same oil, this home-made pigment makes paint which is even leaner, probably because of the larger, coarser particle size.

It's extremely stringy and thixotropic, and produces dense, opaque layers even when quite liquid. When you use it, you quite often find yourself getting little flashes of realization of why certain details in old paintings look the way they do.

It's very slightly darker than industrially produced lead white, let's say 95% the brightness. I've found that in an actual painting that value difference is meaningless, especially since this paint will yellow less due to its lower oil absorption. It has really only one noticeable disadvantage compared to the industrial lead. With industrially produced lead carbonate, I know of at least one kind of oil which will make fairly crisp paint, minimizing the leveling quality while retaining the stringiness and thixotropy, preserving quite crisp brush strokes and textures. This stack process lead, however, doesn't work as well; it has a much greater tendency to be enamel-like. I think this might be another result of the larger particle size; industrially made lead white (which I think is made by electrolysis) has a different crystalline structure and is significantly finer.

 

Egg Yolk Emulsion

The enameling quality is often useful, of course, and is often not an issue anyway if the paint is applied thinly. Before the 19th century, this pigment was really all anyone had. But heavy, crisp impasto was possible long before then, if not very common. Rembrandt used a lot of it in his later pictures. How did he do it? The one way I know of for certain is by emulsifying a little egg yolk into the paint. If you've ever tried it with some melting, slumping lead paint, you know that it turns it crisp and manageable, without decreasing the stringiness too much...

 

Replacing Egg Yolk?

...but if you've ever tried it you might also know that egg yolk is a bit of a pain. It dries too quickly if you leave any on the palette by itself, and you can't store it very long because it goes bad. I've tried freezing it... which doesn't really work very well.

Is there something better you can use instead of egg yolk? There might just be, though I'm not completely sure yet. I started to think about acrylic resin... it's water based, and can have a similar consistency to egg yolk, or a much thicker one, depending on the formulation. It also cures irreversibly, like egg tempera, rather than simply drying by evaporation; in fact, it's likely considerably tougher and more water resistant.

I tried mixing a little acrylic matte medium into my home made paint, and it did not work well. But I also had some old Liquitex high-viscosity titanium white paint lying around, so I tried that. It worked... it made thick yet manageable crisper paint which was still very stringy. I certainly haven't used it on an actual canvas yet, but the test samples I made have dried to be hard and durable, possibly more so than ones with egg. I suspect it will make a tougher layer, not a weaker one.

The fact that there's a little titanium dioxide in this mixture might mean that it's especially good for heavy impasto highlights, since it should boost the brightness very slightly. But it might also alter the way the lead interacts with other colours. Titanium is much more opaque than lead white, and is liable to make nasty chalky tints when mixed with other colours.

So the next obvious thing which I haven't tried yet is to get some high-viscosity, heavy acrylic gel. Acrylic gel is transparent and has no pigment or filler... it's thick and shouldn't interfere with the colour. It might be perfect...

I hope it works...

 

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