Blackboard Fonts In newtxmath

Question

I read a similar question in another thread (regarding kpfonts) but could not apply the solution to solve my problem. I'd like to use newtxmath blackboard fonts instead of the usual ones. Is there an easy way to load them? I'm using XelateX. Thank you and regards.

\documentclass[14pt, a4paper, reqno]{extarticle}

\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage[lite]{mtpro2}
\usepackage{mathspec}   % https://ctan.org/pkg/mathspec     

\setmainfont{Old Standard}
\setmathsfont(Digits)[Scale=0.9]{Old Standard}
\setmathsfont(Latin){Old Standard}
\setmathsfont(Greek)[Uppercase=Regular,Lowercase=Regular]{GFS Didot}
\setmathrm{Old Standard}

\usepackage[bb=tx]{mathalpha}


\begin{document}

$F\, (x_{\, 1},\dots ,x_{\, n})$ $\mathbb{R}$ $\partial$  $\sum$

\end{document}

Answer 1

Load \usepackage[bb=px]{mathalpha}, possibly with a bbscaled= option. You might also try bb=txof for the outline font.

ETA: As of June 2021, the bb=tx option of mathalpha is broken. You can try whichever of the others you like, redefine \mathbb in the same complex way as newtxmath.sty, or, most simply, use unicode-math instead of mathspec. This lets you add the command:

\setmathfont{TeX Gyre Termes Math}[range=bb, Scale=MatchUppercase]

STIX Two Math would be another good choice here.

Answer 2

Unfortunately mathalpha is buggy.

You can directly set the math alphabet in a similar way as newtxmath does.

%\documentclass[14pt, a4paper, reqno]{extarticle}
\documentclass{article}

\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage[lite]{mtpro2}
\usepackage{mathspec}   % https://ctan.org/pkg/mathspec     

\setmainfont{Old Standard}
\setmathsfont(Digits)[Scale=0.9]{Old Standard}
\setmathsfont(Latin){Old Standard}
\setmathsfont(Greek)[Uppercase=Regular,Lowercase=Regular]{GFS Didot}
\setmathrm{Old Standard}

\DeclareMathAlphabet{\mathbb}{U}{ntxsym}{m}{n}


\begin{document}

Some text \emph{x}
$F\, (x_{\, 1},\dots ,x_{\, n})$ $\mathbb{R}$ $\partial$  $\sum$

$\mathbb{ABCDEFGHIJKLMNOPQRSTUVWXYZ}$

\end{document}

Compare the list of blackboard bold letters with the following picture

which has been obtained with pdflatex and the file

\documentclass{article}
\usepackage{newtxmath}

\begin{document}

$\mathbb{ABCDEFGHIJKLMNOPQRSTUVWXYZ}$

\end{document}

They look exactly the same, don't they?