# Origin / first use of $\mathbb{Z}$ (blackboard bold Z)?

I'm aware that the choice of "Z" comes from German zahlen (for "numbers"); however, I was curious to know when the dedicated font, which I believe is called "blackboard bold" was introduced?

The Wikipedia article on blackboard bold is poorly documented on this point (i.e. specifically the introduction and wide adoption, in print; indeed one of the two links provided in support of their claims is broken). Does anyone have suggestions for a better source on this topic?

• The broken link is to Lee's 2003 post:"It is my impression that such symbols were first used in polycopied/mimeographed notes... I have exchanged e-mail with Professor Gunning... he says he picked it up in the Kodaira-Spencer seminars (at Princeton, early 1960s), and that someone there (whose name he can't recall) attributed it to Bourbaki. He confirms that it was in the early 1960s that he himself was converted to the notation, and started passing it on to students". – Conifold Apr 26 at 4:35
• @Conifold thank you for sharing that! His post was really interesting. – Rax Adaam Apr 27 at 16:05

## 1 Answer

Part of @user6530's answer to this related question about the use of Q and $$\mathbb{Q}$$ for the rationals discussed the use of blackboard bold, so I thought I'd share it, here, for those interested:

Now, some words about Bourbaki. Yes, "they" uses 𝑄 for rational numbers, and no, they does not use blackboard bold ℚ (at least in 1940s papers). An early occurence (maybe the earliest printed on paper) of 𝑄 to denote the set of rational numbers is here at page 3 in the number 5 (7-10 December 1940) of La Tribu, the Bourbaki's internal newsletter. We read

𝑄 est ordonné [...] Topologie de 𝑄 [...] Complétion de 𝑄 : nombres réels

so there is no doubt that here 𝑄 refers to our ℚ. Clearly, we find 𝑄 for rational numbers in the 1942 Algèbre (from page 29).