Change the equation font locally

Question

I want to change the equation font to mathbf in a single equation environment, equation or align.

How do I do that? I tried

\begin{align}
\begin{mathbf}
equation1 \\
equation2
\end{mathbf}
\end{align}

and

\begin{align}
\mathbf{
equation1 \\
equation2
}
\end{align}

with no luck. It seems as if \\ breaks the \mathbf environment..?

Answer 1

For making a complete environment bold, you could use the switch \boldmath. \unboldmath switches back.

\boldmath
\begin{align}
  ax + by + c &= 0 \\
  ax - by &= xy
\end{align}
\unboldmath

If \bf is available (base classes still define it), \everymath{\bf} before the align environment switches to the \mathbf font for the complete environment. Of course it could be done without \bf, but it would be the quickest way.