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. 
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
