As far as my knowledge reaches, the composition of leading could vary as much as the composition of the sorts themselves. Making it pure lead would make it easier to cut, but it would also be easier to accidentally bend in the long strips, and it would be much heavier than if it were mixed.

I'm sure it depended on the specific letterpress. Leading wouldn't really need any "harder" metals as it doesn't receive much eroding over time, so maybe many left out other metals as they were more costly.

Matthew — I checked a few references I have here and couldn’t find specific information about type metal for leads. The 1923 ATF catalogue offers 1-point leads in brass (presumably, you want 1-point leads a bit harder) and the rest in “metal,” without elaboration.

You should try contacting Theo Rehak. He would undoubtedly know, or be able to give a very educated guess. Nick Sherman might have contact information for Rehak. Nick’s helping a couple guys who are working with Theo to revitalize the Dale Guild Type Foundry (a true metal foundry, not just in name).

in brass (presumably, you want 1-point leads a bit harder)

Different metals for different thicknesses was also intended to make identification by the compositor easier, I think.

That was certainly true of spacing matter (coppers, brasses, thins, and thicks). Not sure if the same principle applied to leads. Maybe so.

Leading and other strip materials for letterpress are generally cast from an alloy that has a higher percentage of lead, so is cheaper to buy, usually about the same alloy as what was used for Linotype metal (since Linotype slugs were generally printed from once and then melted down to recast; they didn't need to be hard for repeated reuse).

I have never seen 1 pt. brass leads - too expensive! It's very easy to tell the difference between 1 pt. and 2 pt. leads when you have them in hand.

The 1 and 2 pt. leads will flex just because they are long and thin compared to lead type. A 6 pt. slug of the same length will not noticeably flex.

As far as I remember from my Art School days when we used loose type, the thinner ones were made of brass and quite delicate.

Thicker ones of a kind of light metal (might have been an aluminum alloy) and the even thicker ones, including the material to lock up the composition were made of an ironlike metal where a lot of hollow interior shapes were used to lighten the weight of these elements.

I have one of the medium (alu?) ones somewhere, but I guess having that tested for its composition is out of my reach…

Bert, its weight and dimensions(*) (as exactly as you can get) ought to tell you if it's massive alumin(i)um or an alloy.

(*) Or maybe a revisit of Archimedes' gold crown party trick.

Aluminum is 0.098 punds per cubic inch.

For improved stability, rigidity, machining or extruding characteristics, resistance to corrosion or reduced cost, it will almost certainly be an alloy which may or may not have a noticeably different weight but for the volume of metal you have, the difference would be within a rounding error.

The leading I used in school was an alloy, like the type.

Cheers!