LEAD WHITE
courtesy of Natural Pigments.com
 

Below you will find a fascinating photo journal of the traditional and ancient process of making lead white  pigment, exactly the same as would have been done in Rembrandt's time and which the company Natural Pigments very kindly posted on their forum page.

Natural Pigments decided to make lead white according to the stack method (also called Dutch process), not because of any immediate shortage of basic lead carbonate, but because this method makes a significantly distinctive pigment that has different properties in oil. They believe (as I do) it is important for artists today to be able to experience this pigment and to use it in their artwork.

Modern commercial tube versions of lead white do not behave in the same way or give you the same effects, no matter how much you pile into the highlights. Its taken me years to understand this.

 
     

A "stack" was built that accurately reconstructs the so-called "Dutch method" of making white lead. This method involved corroding metallic lead in earthenware pots on stacks of manure to make basic lead carbonate. The method was employed since antiquity up until the middle of the 20th century with few significant changes. The pictures following show some of the stages in building the stack or what is called the "blue bed."


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A shed was built to house the stack and control the environment in which the lead corrodes. Redwood bark (bags seen at right) was used to improve drainage and aerate the horse manure.


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Strips of lead sheet were cleaned and rolled into spiral coils before loading into earthenware pots. Coils of lead sheet were more common in 16th century Dutch white lead works than were lead "buckles." The buckles were often used together with lead sheets, especially in 18th century England and afterwards in the U.S., just as tan bark replaced stable-litter (horse manure) in many of these lead works.


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Specially made earthenware pots were first arranged and then filled about one-third with vinegar. The differently colored pots indicate different amounts of lead or lead that we processed differently. We next placed the rolled lead coils into the pots. Some pots had covers as part of our attempt to understand the corrosion process described in old literature.


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Fresh horse manure collected from a local stable was mixed with bark and placed in layers inside the shed.


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The corroding pots were transferred from the staging area to the shed and embedded in the horse manure.


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Nearly half a ton of lead in pots was deposited over the three-foot high bed of horse manure. It takes about 12 weeks for the lead to completely corrode and form white lead.

Week Two

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The stack shed is located in a remote area where the outside temperature varies from 5 C. to 25 C. The temperature will continue to fall as the winter approaches.


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Stack pots after two weeks of corroding. The smell of acetic acid (vinegar) is still present inside the stack shed, but not as sharp as it was initially. The temperature within the compost heap is raising, but on the surface it is still at ambient temperatures. The relative humidity inside the shed is nearly 100%. Controlling the compost stack temperature is critical to maintaining conditions suitable for lead corrosion. We developed an innovative methd for maintaining the temperature inside the shed.


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A close view of the coils shows the extent of corrosion on the lead after only two weeks, yet unevenly spread across the lead sheet. This was a problem often discussed in literature but without solution.

Natural Pigments will offer two grades of the pigment, one that they call "Flake White" and the other simply "Stack Lead White." The distinction is in how the two are processed.

The first grade, Flake White, will be composed of the actual flakes that fall off of the lead sheets with little processing except for washing to remove traces of lead acetate. This grade will require some grinding in order to use in paint, but will afford some interesting experimentation by artists.

The second grade, Stack Lead White, will be composed of the flakes and the white lead that is mechanically removed from the rolls by either knocking off by hammer or scrubbing off by brush. This grade will be washed and ground ready for use without further grinding by the artist.

Natural Pigments

 

 

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