The railroad used jointed rail like we use at Rail Yard Studios. And while it is still quite common, increased load sizes and standards for track maintenance require continuous welded rail (CWR) or ribbon rail as it is also called.
We use the kits in these boxes to create those long pieces of uninterrupted rail.
At the joint where two rails come together, It starts with a mold. Add some packing clay to fill in any gaps around the mold, and then the ends of the rails are heated to glowing a brilliant orange red.
Place a clay pot on top filled with steel pellets along with a bit of thermite (really powerful stuff - no joke) and toss in a lit ignitor and the pot full of metal pellets becomes a lava-like flow of molten steel filling the void between the two rails and bonding them together.
We love the old school jointed rail. But seeing the crew pull off these modern-day welded joints, well, it is simply fascinating.