I've used the 24 karat gold mica with TD white and it clumped...small little clumps but clumps none the less. Since it's getting washed off I don't think the glitter will leave any "radiance" like you might get with a lotion or other leave on product. Here's a pic of my soap with the gold mica mixed in the white. You can see the clumps even from the distance:
I have a silvery white mica that will make soap slightly shimmery but adding TD would only cover up the shimmer and none of the shimmer stays on the skin.
If you really want shimmery skin, buy some clear aloe gel and mix your mica or fine body safe glitter into that. If you must have shimmery soap, you need a very clear melt and pour base but it still won't glitter your skin.