# Bolder Blackboard bold

I am looking for bold versions of the blackboard bold letters. Unfortunately, the best symbols I have come up with so far are hard to distinguish from the usual blackboard bold letters. Is there a way to obtain even bolder blackboard letters?

My best attempt so far:

\documentclass{article}

\pagenumbering{gobble} % switch off page numbering

\usepackage{amsmath}
\usepackage[bb=boondox]{mathalfa} % for mathbbb

\begin{document}
\begin{align*}
\mathbbb{B} & \mathbb{B} \\
\mathbbb{C} & \mathbb{C} \\
\mathbbb{N} & \mathbb{N} \\
\mathbbb{P} & \mathbb{P} \\
\mathbbb{Z} & \mathbb{Z}
\end{align*}
\end{document}

• In my opinion, blackboard bold should only be used to write on blackboard. Bourbaki uses \mathbf. Nov 17, 2021 at 11:11
• @Bernard Thanks for the suggestion on using \mathbf instead. In my domain-specific context, bolder blackboard font would be preferable, but \mathbf could be a fall-back option. Nov 17, 2021 at 11:30
• there are loads of double struck fonts available (try stix2 package for a darker \mathbb) if you use luatex or xetex any Unicode math font has these so you could try stix, Cambria math, TeX Gyre Termes Math etc. with input ℂℕℙℤ Nov 17, 2021 at 11:35
• @DavidCarlisle Using luatex/xetech is hard in my context (it would require getting many people to reconfigure their system). Does this mean that I cannot use this approach? Nov 17, 2021 at 13:01
• Put a contour package output comparison, too. Unrelated: any non-font solution to a font question will look fake in some corner somewhere. Sounds like you are after a variable font (but again, that takes you away from pdflatex). Nov 17, 2021 at 14:27

Based on the comments to the original question, I have compiled a list of options below. No option is perfect so far:

• "Bold" is not blackboard bold
• "mathbbb" and "kern" are both hard to distinguish from normal "mathbb"
• "kern" and "more kern" have a rendering artifact at the tips of "C"
• "contour" looks weird when scaled down a lot (but it is the best so far)

\documentclass{article}

\pagenumbering{gobble} % switch off page numbering
\usepackage[landscape,margin=1in]{geometry}

\usepackage{amsmath}
\usepackage[bb=boondox]{mathalfa} % for mathbbb
\usepackage{stix2}
\usepackage{xcolor}
\usepackage{contour}
\contourlength{0.02em}

\usepackage{amsfonts}

\newcommand{\mathbbkern}[1]{%
\ooalign{$\mathbb{#1}$\cr$\mkern0.5mu\mathbb{#1}$}%
}
\newcommand{\mathbbkernmore}[1]{%
\ooalign{$\mathbb{#1}$\cr$\mkern0.5mu\mathbb{#1}$\cr$\mkern1mu\mathbb{#1}$}%
}
\newcommand{\mathbbbkern}[1]{%
\ooalign{$\mathbbb{#1}$\cr$\mkern0.5mu\mathbbb{#1}$}%
}
\newcommand{\mathbbbkernmore}[1]{%
\ooalign{%
$\mathbbb{#1}$\cr%
$\mkern0.05mu\mathbbb{#1}$\cr%
$\mkern0.10mu\mathbbb{#1}$\cr%
$\mkern0.15mu\mathbbb{#1}$\cr%
$\mkern0.20mu\mathbbb{#1}$\cr%
$\mkern0.25mu\mathbbb{#1}$\cr%
$\mkern0.30mu\mathbbb{#1}$\cr%
$\mkern0.35mu\mathbbb{#1}$\cr%
$\mkern0.40mu\mathbbb{#1}$\cr%
$\mkern0.45mu\mathbbb{#1}$\cr%
$\mkern0.50mu\mathbbb{#1}$\cr%
$\mkern0.55mu\mathbbb{#1}$\cr%
$\mkern0.60mu\mathbbb{#1}$%
}%
}
\newcommand{\ccontour}[1]{%
\colorlet{contour-saved}{.}%
\contour{contour-saved}{#1}%
}
\newcommand{\mathbbcontour}[1]{
\ccontour{\ensuremath{\mathbb{#1}}}
}
\newcommand{\mathbbbcontour}[1]{
\ccontour{\ensuremath{\mathbbb{#1}}}
}

\begin{document}

\begin{align*}
\begin{array}{ccccccccccc}
\text{Normal} & \text{Bold} & \text{mathbb} & \text{mathbbb} & \text{kern} & \text{more kern} & \text{mathbbb + kern} & \text{mathbbb + more kern} & \text{contour} & \text{mathbbb + contour} \\
%
B & \mathbf{B} & \mathbb{B} & \mathbbb{B} & \mathbbkern{B} & \mathbbkernmore{B} & \mathbbbkern{B} & \mathbbbkernmore{B} & \mathbbcontour{B} & \mathbbbcontour{B} \\
%
C & \mathbf{C} & \mathbb{C} & \mathbbb{C} & \mathbbkern{C} & \mathbbkernmore{C} & \mathbbbkern{C} & \mathbbbkernmore{C} & \mathbbcontour{C} & \mathbbbcontour{C} \\
%
N & \mathbf{N} & \mathbb{N} & \mathbbb{N} & \mathbbkern{N} & \mathbbkernmore{N} & \mathbbbkern{N} & \mathbbbkernmore{N} & \mathbbcontour{N} & \mathbbbcontour{N} \\
%
P & \mathbf{P} & \mathbb{P} & \mathbbb{P} & \mathbbkern{P} & \mathbbkernmore{P} & \mathbbbkern{P} & \mathbbbkernmore{P} & \mathbbcontour{P} & \mathbbbcontour{P} \\
%
Z & \mathbf{Z} & \mathbb{Z} & \mathbbb{Z} & \mathbbkern{Z} & \mathbbkernmore{Z} & \mathbbbkern{Z} & \mathbbbkernmore{Z} & \mathbbcontour{Z} & \mathbbbcontour{Z}
\end{array}
\end{align*}

\newpage

\begin{align*}
\arraycolsep=2pt
\begin{array}{cccccccccc}
C & \mathbf{C} & \mathbb{C} & \mathbbb{C} & \mathbbkern{C} & \mathbbkernmore{C} & \mathbbbkern{C} & \mathbbbkernmore{C} & \mathbbcontour{C} & \mathbbbcontour{C}
\end{array}
\end{align*}

\end{document}


Here is a magnified version of kern and contour versions of ℂ, to show the rendering artifact:

I’m not sure whether you’re asking for two different weights of blackboard bold in the same document, or for a heavier blackboard-bold font.

### Selecting a Heavier Blackboard Bold

I would first check the font samples in the mathalpha manual, if you are using PDFTeX. If you can use unicode-math, you can select a different weight of \mathbb with a command such as

\setmathfont{KPMath-Regular}
\setmathfont{KPMath-Semibold}[range=bb]


If your math font does not come in a bold version, you can fake one with something like

\setmathfont{NewCMMath-Book}
\setmathfont{NewCMMath-Book}[range=bb,
FakeBold=0.05]


You can make the blackboard bold heavier by increasing the number after FakeBold=.

### Using Two Weights of Blackboard Bold

The mathalpha package supports \mathbbb for bolder-blackboard-bold. It only works for certain fonts.

Many other packages, including unicode-math and bm, allow you to write \boldsymbol{\mathbb{N}}. This requires you to have a bold math version defined. Normally, your font package will do this for you. If the math font you load with unicode-math has the weights -Regular and -Bold, the package will automatically load the latter as your bold math font.

You can also set this up manually, with commands such as

\setmathfont{KPMath-Light}
\setmathfont{KPMath-Semibold}[version=bold]


In legacy 8-bit TeX, you would set the bold math version for blackboard bold with a command such as

\SetMathAlphabet{\mathbb}{bold}{xyz}{U}{m}{b}


In either case, you could for convenience define a command

\providecommand\mathbbb[1]{\boldsymbol{\mathbb{#1}}}