Making Dutch Lead White :: Paintings

Making Pigments - Dutch Lead White
Sometimes, you need to have something that you can't get anywhere.

Before we get started...

SAFETY FIRST.

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.

Dutch Lead White

What is lead white? Lead white can be found in nature as the mineral 'hydrocerussite' but it has been made artificially for so long that the man-made version is found just about everywhere since lead has been smelted. Apart from hydrocerussite, Lead white is the white compound that you get from weathered lead pipes/roofing. It is what happens when lead metal has a chance to react with the environment over a long period of time. Pipes and roofs are quite resistant to corrosion so thousands of years ago, someone found a way of speeding it up.

First of all, this is what lead white is...

2 Pb CO₃-Pb (OH)₂

for the non-chemist, hover the mouse over
the parts of the formula to see what they are.

You can see from the formula that it is a lead compound of atmospheric water and carbon dioxide.

The formula weight of this is 755.6g/mol with three lead atoms at 208g/mol so 100g of lead metal will make roughly 121g of white lead pigment.

The reaction goes like this:

exposed metalic lead is attacked by acetic acid vapour in the presence of oxygen and water vapour (the latter allowing the acetic acid to be an acid as opposed to just an organic solvent) and forms lead acetate;

carbon dioxide in the air displaces the acetic acid to make lead carbonate

water in the air replaces acetic acid to make lead hydroxide

the acetic acid goes on to attack the metalic lead further

This reaction will happen without the acetic acid there - commercial lead sheet for roofing has a protective compound on the surface to help prevent this from happening - but it will happen painfully slowly. The acetic acid acts as a catalyst - changing the rate of reaction - in this case speeding it up enormously so instead of taking 100 years to eat a hole in the sheet, it will all have rotted through in somewhere between 6 months and a year, depending upon your climate.

So, what do we need and where can we find it?

Lead sheet - the reaction happens on the surface so the larger the surface area to mass ratio, the more we produce for the lead we buy in a given time;

Acetone - this is to remove the labelling from the lead sheet and also any protective layer from the surface of the lead;

Acetic acid - as said above, this is the catalyst for the reaction. You can buy glacial acetic acid online fairly easily. It is called 'glacial' because pure acetic acid freezes at 16.6C which is only a few degrees below room temperature and during winter, it will freeze solid. Glacial acetic acid is 100% acid and although it is the same acid that is in vinegar, that is only 5% so sprinkling glacial acetic acid on your chips (fries in the US) is both dangerous and an act of sheer stupidity;

Containers that are rugged, watertight and corrosion resistant

plastic spacers - you can make these out of old pop bottles; and,

If you are in the UK and the same happens to you as it did to me, you will also need:

a length of silicone tubing (5-10m depending upon circumstances);

an old 2 litre pop bottle;

ordinary granulated sugar;

yeast;

Later on, you will need:

solid sodium hydroxide;

solid sodium carbonate;

a dedicated mortar and pestle;

filter papers;

a funnel; and

plastic jars.

as well as rubber gloves, goggles apron or lab coat and so on.

So, we can buy lead and acetic acid that are pure enough, water comes out of the taps and there is oxygen and carbon dioxide in the air. Whilst the oxygen level is a nice 21%, the CO₂ level is only around 400ppm which is far to low so we need to increase that quite substantially - we need a carbon dioxide generator.

'Really Useful Boxes' produce boxes that are rugged and made of the right materials for this project so I got a large one and four smaller ones that would fit inside. The idea was that I would put a carbon dioxide generator in one of them, leaving the others to put lead spirals in.

You can get lead that is suited really well to a project like this in the form of 'Code 3' lead strip which I got online as a 3m roll at 150mm wide (7kg of lead ~ £850-£8,000 worth of lead white depending upon whom you buy it from). Code 3 is 1.32mm thick which translates to 14.97kg/m². Here, I'm making it only for my own use, I am not selling it on (or even giving it away) so I don't need to make that much of it in one go. I can use the plant to make a kilo or so then put it somewhere safe until around 18 months before I need some more.

To prepare it, I removed the sticky label with a knife then some acetone to remove the remaining glue. Then, I scrubbed the surface to remove dirt, lead oxide and anything that might be there to protect the surface then I swabbed it with acetone again to remove anything that I couldn't see - this stuff is supposed to last 100 years but I needed it to go a bit quicker than that.

I cut around 350mm off the roll and cut it down the middle, lengthways to get two strips at 75mm wide totalling around 800g so that I would end up with just under a kilo of white lead pigment.

Next, I rolled them into spirals and placed them on plastic spacers that I had made by zigzag-folding some plastic pop bottle side cut to around 1cm wide strip so that they were a centimetre or so off the floor of the plastic container. The lead coils don't have to be coils, you can have them as zigzags - the only requirement really is that the air can get to them.

In the diagram, the lids of the lower cells have been rested on the tops of those cells sideways so that the atmosphere inside the larger container can move around freely to avoid a situation where each cell has its own micro atmosphere.

Next, I added around 5mls of glacial acetic acid to the bottom of each of the cells that I was using, along with some water.

Now, it was time to generate some CO₂.

I started off with some sodium carbonate (not bicarbonate - carbonate has twice as much carbon dioxide in it per molecule than sodium bicarbonate) to which I added some water to dissolve it and some hydrochloric acid from a toilet cleaning product in one of the cells as per diagram 'A'. It all fizzed nicely so I put it in the office and left it but not a lot seemed to be happening so I checked for the CO₂ level using a lighted taper and there was none. Failure.

Next, I emptied out the cell that I had used for the generator and three-quarters filled it with warm water into which I had dissolved some sugar and then added some yeast. The top of the large container wasn't air tight so oxygen could get in still.

After a couple of days, there were complaints of the smell of acetic acid from it so it had to go outside. Outside, the British climate wasn't warm enough to let the yeast react so that had to be rethought.

So, I got an empty 2 litre pop bottle and two-thirds filled it with warm water into which I had dissolved some sugar and then added some yeast. I had some silicone tubing which I had put through a hole in the bottle's lid, ran down the outside of the building and into the lead plant. The bottle was in the warm and able to generate as much carbon dioxide as I needed. Every 5-10 days, I would change the yeast suspension for fresh and it would keep on going.You can see from diagram 'B' that now, we have enough room for four flake-producing cells.

Renewing the acetic acid and water to replace evaporation and consumption, I kept this up for well over a year.

This is traditional Dutch stack lead flake forming on one of the lead rolls. You can see why it is call flake white. If left, it will grow to between 5mm and 15mm thick but the thicker it is, the less oxygen, acetic acid and moisture can get through to the metal.

One thing that I noticed was that it took a while for the corrosion reaction to get going but once it had taken hold, it just went and went. Once I had finished this, I still had some unreacted lead coil left so I just laid it across the top of two of the cells - without any CO₂ generator or any extra acid and left it. When I looked at it next, a few months later, it had rotted through and collapsed where i had left it. So, if you are having a go at this and it is taking a while to get started, don't worry too much about it.

One thing that lead flake likes to do is to fall off the lead coil, into the acetic acid. When this happens, the acetic acid, which is a stronger acid than the carbonic acid that creates the carbonate, is displaced to make lead acetate which is readily soluble in water. As the water and acetic acid evaporate off, they leave behind the lead acetate which gets so concentrated that lead acetate crystals start to grow and these can end up quite long - I found one that was at least 7cm long.

So as to prevent this, just harvest the lead at regular intervals - every 2-4 months - by carefully taking the coils out and bending them slightly so that the flake falls off into a container to be stored. Put the lead coil back and add some more acetic acid and water - leave the lead acetate in there - it isn't going anywhere.

Once you have enough lead flake that you feel that you can process it, harvest the lead flake and put it with the rest that you have collected and put the lead coils, what is left of them, to one side.

Lead Acetate

Now, you have a container that has lead acetate in the bottom so add some water to the crystals so as to dissolve them. We are not going to throw this away as it can represent quite a bit of lead and also, it is dangerous to the environment to have us making lead compounds and then not incorporating them into works of art.

The intention here is that you remove the acetate and replace it with the same anions that are in lead white - carbonate and hydroxide - but there is something else that you can do instead, although I would recommend that you keep the resultant pigment well separated from the lead white if you decide to follow that route.

Lead Chromate - chrome yellow - an interesting diversion.

If, instead of replacing the acetate with hydroxide and carbonate, you replace it with chromate, you will get lead chromate (PbCrO₄) which is a vivid yellow pigment, the preparation of which was published in 1809.

All you need to do is make a solution of potassium chromate and add that to the dissolved lead acetate then filter it off and wash it, eventually drying it then prepare your paint the same way that you would with any other pigment.

Modern Lead white

Make up some sodium hydroxide solution - be very careful not to get any solid or liquid anywhere. The small beads of this stuff can roll all over the place then react with the moisture in the air to make caustic soda solution which you can then end up getting on you. A small amount of this, even fairly dilute, can cause burns that can blind you or take literally months to heal. I would strongly recommend that the location that you choose to do anything at all with caustic soda pellets/beads is somewhere that can be washed down easily, like the bottom of a sink with a flat bottom, for instance. if you get any on your skin, it will feel soapy so rinse it off straight away with copious water, rubbing the solution as the water runs over it until it doesn't feel soapy any more.

Additionally and in a different container, make up some sodium carbonate solution - this isn't quite as dangerous as the NaOH solution but you still need to make sure that you remove any of it that you might get on you.

It doesn't matter that much how much of each you make as long as there is enough to react - as a rule of thumb, a nice excess (possibly around 2:1 or so) is taking the same volume of sodium hydroxide and of sodium carbonate as there is lead acetate.

Once they are all dissolved and well mixed, add roughly half of the lead acetate solution to the sodium carbonate solution and to the remaining half of lead acetate solution, add the sodium hydroxide solution. It doesn't matter which sodium solution you use first, it is just that by pouring the last one into the lead acetate solution, you are not adding lead to another container.

When you do this, a fine precipitate of lead carbonate and in the other container, lead hydroxide will form, taking out any lead in there. Next, add some water to each, mix them around and then let them settle. Once they have settled, carefully pour off the excess water and sodium salt solution and then add more water and repeat the washing, settling, pouring routine. Next, add some water and mix the two precipitates. You now have a modern synthetic lead carbonate/ hydroxide that isn't flake white although chemically, it is similar. You can decide whether or not you want to add it to the actual flake white that you have made or keep it separate and process it parallel to the actual flake white.

Traditional Lead white

This is what you need to do now that you have your flake white (and to the lead white that you have recovered from lead acetate or chrome yellow that you have made from the lead acetate).

Put your flake white in a container and break up the flake, removing any bits of lead metal as you go and putting them to one side. You can put them back in your container and let the flake reaction continue.

Next, a bit at a time, put some lead flake into the mortar and add some water. Grind it until you think it is fine enough and then tip this into a container. Repeat the process until you have processed all of the lead. Then, add a bit more water and leave it to settle.

Once it has settled, you might notice that the water has a slight blue tinge to it. This is because in the lead process, some copper ends up in the lead roofing as an impurity. As this is water soluble, it is not a problem as it will be removed when you tip the water away. Lead white isn't very soluble in water so you aren't going to lose any appreciable quantity in this process if you have let the water clear properly.

So, tip away that water - it doesn't matter if there is a bit left behind, add some more water, give it a good stir around and let it settle again. Do this several times until you feel happy that you have removed any impurities.

Next, add some water to make a slurry of your now clean lead white. Get a filter paper and filter some of the slurry until you have possibly 10 cubic centimetres of solid flake. Take that filter paper and fold over the top then put it on some kitchen towel. Keep on doing this until you have done all of the flake white.

Fold over the paper towel and gently squeeze the water out of it, replacing paper towels as necessary, until they feel fairly stiff. Then, again, on kitchen towel, but on a flat portable surface such as a tray (you might want to put some clingfilm over the surface of the tray first), arrange the little chunks of lead white, still in their filter papers on the towel and then, over the coarse of a few weeks, let them dry out.

Finally, peel away the filter paper and put them in a plastic jar, weigh it, label it and store it in a dry place away from children and animals - a safe of some sort is probably a good idea for solving ths problem.

Some people leave the lead white to mature - this can really only represent and opportunity for any remaining lead that didn't get taken out to oxidise so that you don't end up with lead metal in your paint.

All images and original artwork Copyright ©2017 Paul Alan Grosse.