After much experimentation I have found one method to make big clear chunks of ice. That method is to put water in a cooler in the freezer, then chop off the top clear layer. Now the trick was to get this into useful sized cubes for glasses.
Starting with the slab of ice (this one about three inches thick),
I used a heated bread knife to score the ice just about 1/8th of an inch,
Then tapped the scratch in several places with an ice pick and found it separated really easily.
And I got the whole thing chopped into long spears.
I use these really long ones in a tall glass
and scored and cut the rest of the spears into big fat cubes.
Hooray! Time for a drink.