How to create disabled state of the font awesome icons? : <p>I am using font awesome icons and I need to have a disabled state of the icons. is there any way to do this. I am also using bootstrap. </p>

<p>This is how I am using icons.</p>

<pre><code>&lt;i class="fa fa-slack"&gt;&lt;i/&gt;
</code></pre>

<p>I just need the icon to look like grayed out.</p>
