Increase font size and making a boldface in mathmode in Latex

Question

How to increase the font size and make a boldface of the whole symbol given above in mathmode in Latex ?

Answer 1

Using \bm command from bm package and \scalebox from graphicx package.

Code:

\documentclass{article}
\usepackage{bm,graphicx}

\begin{document}
\centering

Normal
\[\sigma_{E_{1}}^{(l)}\]

\bigskip

Bold
\[\bm{\sigma_{E_{1}}^{(l)}}\]

\bigskip

Bold and bigger
\[\scalebox{2}{\ensuremath{\bm{\sigma_{E_{1}}^{(l)}}}}\]

\end{document} 

The latter can be used outside math mode, as well. Adjust the factor 2 to meet your needs.

Answer 2

Another alternative without 'scalebox'.

Code

\documentclass{article}
\usepackage{amsmath,bm}
\begin{document}

Normal
\[
\sigma^{(l)}_{E_1}
\]

Bold and Huge size
\[
\Huge
\bm{
\sigma^{(l)}_{E_1}}
\]

Bold and scripsize
\[
\scriptsize
\bm{
\sigma^{(l)}_{E_1}}
\]
\end{document}