Assuming you are wanting to paint glitter makeup, here's a possible way to go about it. The sort of results I got look like this (on a quick render of a Poser figure, so excuse the absence of hair!):

And in closeup:

Here's a quick tut on how to do this.

1. In Photoshop, create a new image - say 64x64. Then draw a diamond shape like so:
   

2. Go to Edit menu -> Define brush preset and give it a name, then click OK. This saves the brush into your brush palette.

3. Choose the Brush tool then select your new brush. In the Brush manager, select these options:
   

Note the spacing set to 120.

4. In Shape Dynamics, choose Size Jitter 20%, control to Off, Angle Jitter to 100%, Control to Off.

5. In Scattering, select Both axes, 450% (or thereabouts) , Control Off, Count 1.

6. In Color Dynamics, set Hue Jitter to 40, Saturation Jitter to 80%.

7. In Other Dynamics, set Flow Jitter to 0%, Control to Pen Pressure.

Now load an image and reduce your brush size to something appropriate - for this image, it was set to 4 pixels. The harder you press with the pen, the greater the flow, so you can fade the glitter as it gets further from the eye (for example).

Choose the desired colour - the glitter will have varying colours either side of that due to the hue jitter. You can reduce or increase the colour variation by altering the amount of jitter. Paint on a new layer and set its blending mode to Screen. For really bright glitter, duplicate your glitter layer and set it to Overlay. Reduce the opacity of either or both layers to tone down the effect. And feel free to experiment with the above settings, you may find much better ones than those.

Hope that helps.

Steve