The recipe:
Non-fibered foundation coat
Mineral spirits (paint thinner)
In a 5 gal. pail with cover, mix about 1 quart to 1/2 gal. foundation coat, with about a gallon of spirits.
The more asphalt you use the blacker the end result and slower dry time, if too thin the results are a "brown" color and won't stiffen the line as much. Start thin and check a piece of your line, you can add asphalt at any time..or thinners, just mix well. This dip will tar lines, nets, rusty implements, chains, traps, etc., makes a decent dark preservative wood stain. Does NOT make a good dessert topping!
Splashes and drops WILL stain clothing, leather boots and your hands permanently, well it washes off your hands eventually. It will dry overnight unless you go crazy with the asphalt..don't, no need.
If you want to camo your single decoy lines, loose coil the gold color nylon twine, and dip half the coil into the dip. You get a blackish brown and gold striped line that disappears in the water.
When your done dipping, cover the pail, it will last forever, you may need to add a little thinners if it lays around for a time to get the consistency you want back.
Commercial netcoat is the same stuff, just a lot more money and you get to pay shipping.