We use the Nail Board seam on larger surfaces.  Sometimes it is not practical to use a piece of aluminum.

Flatten one side of the ice you intend to fuse with the Nail board.  A circular pattern works well

Next, flatten the other surface

Flip one surface onto the other.

Fill a large syringe with cold water

Separate the ice with a screwdriver

Squirt lots of water into the seam using the syringe.

 If your ice is below 15 F you will need to modify this step (add water more slowly)

Quickly remove the screwdriver & watch as the water squishes through the seam.

We used the Nail board method to create most of the seams in this sculpture for Nike