Preheat the oven to 450 degrees.
In a large bowl, sift together the flour, salt, baking powder, and baking soda. Using a pastry cutter, cut the butter into the flour into until the butter is the size of small peas. Using a fork, gradually stir in the buttermilk, taking care not to overmix. Carefully, fold in the lemon zest and blueberries.
On a floured board, pat the dough into a half inch circle. Using a two and a half inch biscuit cutter, cut out 18 biscuits. You will have to re-pat out the dough to cut out all 18 biscuits. Try to handle the dough as little as possible.
Place the biscuits on a heavy shiny baking sheet with a half inch of space between biscuits. Preferably use a pan with only one side. Bake the biscuits for 12 minutes, or until the tops are light brown.
While the biscuits cool on a wire rack, make the Lemon Glaze: Mix together all the glaze ingredients in a small bowl. Add more lemon juice to thin it out, or more sugar to thicken it.