Tag Archives: chemistry

Casting metal type

Let’s cast metal type of this Gothic M

Gutenberg was trained as a goldsmith, so he knew all about how to work with metal—even how to make the tools. Here’s how Gutenberg made type: he got a super-hard metal (steel), a medium hard metal (copper), and a soft metal (tin/lead/antimony).

The punch is tempered steel. The matrix is copper.

Gutenberg shaped letters on the butt-end of a short steel rod—maybe he used tempered-steel files or chisels on the carbon steel rod (steel has different hardnesses depending on how it’s treated). When the letter was shaped he got the steel rod red hot then tempered it by dunking it in cold water so it would be really hard. Now he had a steel punch. He hammered the punch into a piece of copper (softer than steel) so there was an impression in it shaped like the letter.

This is a super-simplified drawing, just to give you the idea.

This copper matrix was fitted into a 2-piece mold that got clamped tightly together. Gutenberg could cast copies of the letter by pouring molten tin/lead/antimony into the mold.

The type.

Watch the videos below to get a better idea:

A demonstration of how copper can be shaped by steel (skip to the 1:00 mark): https://www.youtube.com/watch?v=tXbUDCfreqE
It’s the molds which were the true technological big deal of this process. If you want to get into the details, here’s everything there is to know about them: https://www.circuitousroot.com/artifice/letters/press/hand-casting/literature/index.html

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What’s metal type made of?

A little melting pot and 3 lead musket balls from my dad’s collection.

Johannes Gutenberg was a goldsmith. He knew how to work with metal, so he developed cast-metal movable type. He used an alloy of antimony, tin and lead. Type metal has a relatively low melting point—probably you could melt it on the stovetop DON’T DO THIS YOU GOOFBALLS I DON’T NEED MORE ANGRY PHONE CALLS FROM YOUR MOMS.

On the other hand, this site says you need 1980°F to melt type metal. That’s hotter than I expected. A stovetop only achieves 350° but lead melts at 621.5°. Tin melts at 449.5°. Antimony melts at 1,167°F. I dunno—I can melt solder (lead/tin) with a propane torch to join copper pipes.
Soldiers in the 1700s cast lead bullets in the field using a campfire. Here’s a scene from the movie The Patriot—Mel Gibson melts tin soldiers to make musket balls (I know, I know, old Mel probably has a blowtorch off-screen fired up to 3,000 on the Kelvin scale). When your great-grandfather was a boy, kids used to cast and recast their own tin soldiers. Maybe the antimony gives type metal a higher melting point. As a jeweler, Gutenberg had stoves and kilns in his shop designed to generate plenty of heat.

You can use this kit for cold-casting: https://www.hobbylobby.com/Crafts-Hobbies/Clay-Molding-Sculpting/Casting/Mini-Casting-Kit/p/22251?gclid=CjwKCAjwzruGBhBAEiwAUqMR8LvgJH4XhS98M-pZUqhaEPE-KWDQQ-2RNBaSmplBNAmv_s4KQ0HIjhoCS8IQAvD_BwE

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