title: Make a 3D model transparent
body: <p>How can I make a specific 3d model transparent? Is it as simple as changing the opacity of the model's material?</p>
  
  <p>I tried the following:</p>
  
  <pre><code>SolidColorBrush br = (SolidColorBrush)matDif.Brush; //matDif = DiffuseMaterial
  br.Opacity = 0.3;
  </code></pre>
  
  <p>When it tries setting the opacity it says that it is in a read-only state and cannot be changed?</p>