Gas/Air Escape Route?

Just when I thought I had the bubble pattern when using chunky, clear frit figured out, the trials below proved me wrong.   As you look at the first example, notice the large number of clear, chunky frit pieces in the lower left-hand quadrant.  There are a minimum of seven good sized frit chunks, and yet only a couple of small bubbles over this area. 

Bottom layer  - reactive clear, next layer - cyan blue fine frit, French vanilla fine frit, and large clear frit, topped with clear COE 90.

 In the previous examples in which a grouping of large, clear frit resulted in large air bubbles directly above the center of the frit, the chunks were centrally located in the piece.  In the example above, the chunks are much closer to an edge.  Is it possible that there was an equivalent amount of gas/air release, but the proximity to the edge allowed the gas/air to escape before gravity and heat did their work to seal the escape-route?  The bubbles that have remained are toward the outside edges of the area.......

Bottom layer  - reactive clear, next layer - cyan blue fine frit, French vanilla fine frit, large clear frit, and fregments of sliver foil, topped with clear COE 90.

 As with all glass firings, there are many variables that play into the effects achieved in the final piece.  In the piece above, the area to the middle-lower left with large, clear frit chunks is bubble free, but the similar area toward the top left has several bubbles - a couple pretty large.   Although it looks like the bubbles are attempting to escape upwards, the piece was actually fired horizontally.g   The grayish material in between these two areas is not frit, but fragments of silver foil.  This, too, could be a reactive location creating the need for a gas/air escape route!

Bottom layer  - reactive clear, next layer - cyan blue fine frit, French vanilla fine frit, and large clear frit, topped with clear COE 90.

To minimize the variables, both this batch of trials and those in the previous blog were fired together, so speed of heating, cooling, or other interior kiln conditions were similar for all of these pieces.