Book review of

Principles and Practices
by Dr. John A. Seim

Primitive iron has been produce on earth now around three millennia. With better smelting procedures and the controlled introduction of carbon to iron, reasonably pure, usable steel has been with us perhaps a thousand years or so. Controlling the carbon content and alloy accurately in steel is a more youthful development in history, perhaps on an industrial scale only in the last couple of centuries. Early firearms manufacturers did not have dependable through-hardening steels and depended on two things to make firearms durable and safe: case hardening and mass. By case hardening (carburizing) the surface of low-tensile steels, they could be made wear resistant but no stronger. ‘Stronger’ meant ‘more’ which is why an 8-bore double rifle from the 1880s will weigh twice as much as a .458 Winchester Magnum rifle from the 1980s that generates similar horsepower.

Surface carburizing of low-carbon steel is a simple process. Steel parts are packed in a steel box and surrounded by some sort of carbon-rich agent such as bone, charcoal, leather bits and the like. Heated to red hot, carbon migrates into the steel. Time in the box determines the depth of carbon flow into the steel. The hot part is dumped into a quench (usually secret recipe involving water) at which time the surface becomes glass-hard to the depth of carbon migration. The resulting part is not really stronger but is enormously shock and wear resistance, thanks to the softer core and extremely hard surface In low-pressure firearms, it is an ideal result.

At the start of the Nineteenth Century, some brighter light discovered that clean, degreased steel packed in charcoal and quenched in a magical, quench, probably aerated water charged with eye-of-newt and faerie dust, produced a mottle display of the various heat colors observed in white steel heated through a range of moderate temperatures. These wondrously interwoven splotches and spills of brown, blue and plum, maybe even a little green and red, are relatively random, depending on the section of the part and disparate rates of cooling. Simple as it sounds, the tricky part (isn’t there always one?) is getting these results predictably, consistently and safely without damage to part or end user.

Gunmakers, often high priests of the gods of technology, often as not practiced a secret liturgy devised to insulate ordinary believers from peculiar knowledge. It was enough to know coloring could be done. Just not how. Consequently, there is still much mystery around the craft. John Seim sets about to dispel some of the darkness by systematic experimentation and research over the course of thirty-plus years. In cahoots with several custom gunmakers, the gunsmithing staff and students at Trinidad State Junior College in Colorado, he presents the results of this ongoing study in his book Colour Case Hardening of Firearms.

While Seim specifically disclaims that this is a ‘how-to’ book, he covers in detail any of a number of critical considerations in the production of bright, stylish coloring. There are discussions of charcoal selection, racking parts, shielding to enhance color and dispersion, quenches and quenching and more.

As one might imagine, there are a number of safety cautions that touch on materials and proof testing. While I am aware of experiments in traditional pack-hardening and coloring of through-hardening materials such as 4140 that involve drawing or tempering after the fact, there are real limitations to the classic pack-hardening methodology. As a general rule, true case hardening with traditional carburizing agents is applicable only to low-carbon steels. Applied to high-carbon steels heated to their critical point (the temperature at which they will achieve maximum hardness for their alloy upon quenching), the parts will be hard through and very brittle, subject to failure at the shock of firing. At this writing, I am aware of only one source of coloring for medium-carbon steels that does not affect the underlying metallurgy. The proprietary process of Turnbull Manufacturing is safe for modern firearms such as Ruger revolvers, reproduction lever guns from Winchester and Browning and similar guns. There are also some molten salt processes which which do not approach closely most steel’s critical point and are therefore suitable.

Only the rare serious student or practitioner will fail to take new or useful information from this book. The curious layman will see through the window of these pages an highly developed and refined but still arcane art and come away with a heightened appreciation of the knowledge and skill that feature in great gunmaking.

Colour Case Hardening of Firearms is 182 pages in bench-friendly spiral-bound form. It is heavily illustrated in color with graphs, charts and tables. and charts where appropriate to elaborate on data. The suppliers list and bibliography are invaluable and encompass much of the necessary intelligence available on the subject.

Price is $75USD post paid. To order, send certified check or international money (no USD money orders from the USPS, please) to:


Dr. John A. Seim
P. O. Box 167
Monarch, Alberta,


Also available at; price and shipping costs may vary. All proceeds from the book sales are donated to the Trinidad State Junior College Alumni Fund to fund new equipment and a new gunsmithing instructor’s position at Trinidad State Junior College in Trinidad, Colorado.