In the real world, coal wagons are either full or empty, with probably equal proportions of each. However, the proprietary model world seems to be populated by wagons that are empty. If a manufacturer does deign to provide something to put in the wagon, it usually looks nothing like the real thing.

To make a load of coal look realistic, there is nothing like using the real thing, but a 25 rake of coal wagons, each filled to the gunnels, would be quite a load for a model locomotive and would probably mean that it would expire before many circuits. So how do we ameliorate this?
After much experimentation, I decided to try foam rubber. The advantage of this material is that it can be cut to fit the wagon and if cut marginally oversize, its natural resilience means that it will stay firmly in the wagon, even when inverted. The big problem was how to get the coal to adhere reliably to the foam.

The procedure is as follows and although tried and tested for use with 2mm scale wagons, there is no reason why it cannot be used for 4mm, or even bigger scales

Firstly, procure a supply of foam rubber, preferably dark grey or black and as dense as possible. If grey or black is not available then try soak the foam in permanent black ink and dry. Cut the foam into strips which are marginally larger than the wagon, but are 1-2 mm less than the internal height. Carefully chamfer the top edges and make the top a little uneven.

Now for the coal. Obtain a few small pieces and roughly crush. Use a kitchen sieve and then re-crush the rejects. Continue doing this until you have enough (a small lump of coal makes a surprising number of loads). Use various sieve sizes to get the size of coal you need remembering that coal as supplied was anything up to 6” in diameter (1mm in N gauge, 2mm in OO).

The coal now needs sticking to the foam formers. To do this I place them on a large sheet of newspaper, right way up, and carefully coat with spray adhesive. Once coated, transfer, to a clean sheet of paper. Then cover with a good layer of the aforementioned crushed coal and press lightly down. Leave to dry for a few minutes and check that the covering is to your satisfaction. If not, lightly spray again and add further coal.

It is best to leave the coal covered foam to ‘cure’ overnight before installing in your wagons. The advantage of this method is that it is light, looks good and, if necessary, the coal load can be easy removed.