Step 1: Go on a trip
You don't have to try so hard. Sand can be dyed with food colouring or you can use 'decorator sand' (the type they put in candle holders).
Also, buy two photo frames while you're out. Here I used 8" by 10".
Step 2: Prep
Clean your glass from the frames you bought. Place one sheet down on your work surface.
Place a spacer in between. I used the backing from one of the frames.
Place your second sheet on top. Take care to line them up well. Put something weighty on top to keep it all in place.
Step 3: Spot weld
Step 4: Fill the gaps
Try not to leave any gaps.
Don't go all the way round!! Gotta leave the top open for sand.
You can also tape the edges for extra security. And to prevent cuts.
Step 5: Tools
I also taped the glass frame to the picture frame backing for ease of sand pouring.
I also also made a bit of a sketch to follow.