Santa Cruz County History - Making a Living

The California Powder Works & San Lorenzo Paper Mill: How Gunpowder Was Made at the CPW
by Barry Brown

Beach Hill
The CPW Wharf at the Foot of Beach Hill, Santa Cruz
Lithograph from Bancroft Library, UC Berkeley


Photograph of Horse-drawn Wagons
Horse-drawn Wagons Loaded With Chemicals
Courtesy of The Museum of Art & History
@ The McPherson Center, Santa Cruz, CA

The gunpowder made at the California Powder Works (CPW) was primarily black powder, a kind of universal explosive used not only in guns but also for blasting rocks and trees and moving earth on construction sites. Black powder consists of approximately 75% potassium nitrate (saltpeter), 12.5% sulfur, and 12.5% charcoal. The charcoal was made locally from the surrounding forests (see Historical Marker #20), but the potassium nitrate and sulfur needed to be imported from Chile, India, or Sicily and were transported via sailing ships which docked at the CPW wharf at the foot of Beach Hill in Santa Cruz (see ill. above).

From the wharf, horse-drawn wagons (see ill., above right) carried the chemicals up Pacific Avenue and through town to the California Powder Works located along the San Lorenzo River. The sulfur arrived in a fairly pure form, but the potassium nitrate required further refining before it could be used. Once dissolved in water, its impurities could be separated and removed.

Photograph of the Mixing House
The Mixing House
Courtesy of The Museum of Art & History
@ The McPherson Center, Santa Cruz, CA

Gunpowder was manufactured as follows:

  1. Equal amounts of sulfur and charcoal were combined in the Mixing House in rotating wooden barrels containing iron balls about 2in. in diameter which pulverized these materials into dust (see ill., right).
  2. This sulfur/charcoal dust was then moved to the Wheel Mills to be incorporated with the potassium nitrate (saltpeter). Here the process first became dangerously explosive. As the rotating wheels crushed the three ingredients together, a fine damp, gray material called mill cake was produced (see Historical Markers #4 & 5).
  3. After a specified time under the wheels, the mill cake was transported to the Press Mill where it was compressed into dense brittle sheets called press cake (see Historical Marker #12).
  4. Press cake sheets were then taken to the Corning Mill where they were broken into grains of various sizes and then sifted through different screens depending on each powder's end use (see Historical Marker #13).
  5. The resulting powders were then moved to the Glaze Mill where their rough edges were removed. By the addition of a small amount of graphite, the powder was made silky smooth and clump-free which facilitated pouring (see Historical Marker #11).
  6. From the Glaze Mill, the powder was taken to the Packing House where it was put in 25 or 50lb. kegs for storage or shipment (see Historical Marker #14 & below).
Photograph of Kegs Inside the Packing House
Kegs Inside the Packing House
Courtesy of The Museum of Art & History
@ The McPherson Center, Santa Cruz, CA

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View similarly tagged articles:

dynamite, powder works, San Lorenzo Valley


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