Ore loads for both the side dump and drop side gondolas were made using cork. It weighs far less than Woodland Scenics or real soil so I could fill the cars without having them weigh a ton. The side dump cars running on the mine loop use chunks of cork coaster shredded by hand into pea size. This represents large chunks coming directly out of the mine. It is hauled around the mountain to a gravity stamp mill where it is crushed before being loaded onto the drop side gondola for the trip to the smelter. To represent the crushed ore I chose ground cork about the size of rock salt. Both loads are made the same way.
There are five loaded side dumps and one loaded drop side car on the layout although they represent many more. I started with weathering the cars. Before the paint could fly I had to do some sanding to reflect the heavy abuse ore inflicts on gondolas. The weight and jagged surface of ore tears the top edges of the cars down fast.The effect can be seen in the examples below along with damage to grab irons. The supports tend to protect the edges giving the side a wavy shape along the top.
In the beginning:
First everything was painted Cibola green and lettered.
I sealed the decals with Tree House Matte finish. When dry the sides were washed top to bottom with black stain. Next the top edge were dry brushed with dark and light grey to look like sun bleached wood. Another coat of sealer was applied and allowed to dry before the final wash of grey stain was applied.
Once everything was dry I lightly sanded down the sides with 100 grit sandpaper to knock the paint off the high edges giving the effect of pealing paint. My evil work was complete with a thin layer of rust ink on the metal hardware.
The inside of the cars would suffer the most abuse and be stripped almost clean of paint by the constant loading and unloading of ore. That means a lot of bare wood with just a little paint surviving near the top edge. I began with a heavy coat of black stain This was followed with dry brushes of dark and light grey. The brush strokes should always be top to bottom here not side to side. This is the direction the ore is traveling as well as rain and grime. The same technique is used along the top deck of the gondola where it will show around the outside.
Another coat of clear sealer was applied to protect the thin washes during reassembly. Once back together a light haze of grey paint was applied around the lower half of the car to represent road grime. I do with rattle can spray paint. The car is placed on work surface at table level outside in direct sunlight. The goal is to create a fog that is mostly dry paint which settles around the base of the car. To do this grey paint, not primer must be used. The air must be perfectly still so the paint will float and the temperature needs to be above 75 degrees. Paint is sprayed from 2-3 feet back in even strokes along the length of the car at roughly wheel level. It is definitely a case of less is more. It may not be readily visible so resist the urge to move closer to apply a heavier coat. Before moving the car apply a coat of matte sealer again. The grey paint is so fine and dry that if you touch the car before sealing it you pull the coating off and leave very distinctive fingerprints in the grime. I learned this the hard way on a boxcar which still has some swirls if you know where to look.
With the car complete and weathered it is time to add the load. While not expensive I did not wish to pour a quart of cork into every car. The bottom of the load fills the car from wall to wall so I started by gluing in a Styrofoam spacer of about a 1/2″. I used TB3 to secure it as there is no real weight involved and the glue bonds quite well to plastic without damaging it. Once the base was in mounded shapes were added to represent the slough of the ore.
Once the glue had dried the foam was painted black to insure no white showed through the relatively thin layer of ore. The ore is a mixture of ground cork, white PVA glue (3/1 mixture with water) and black paint. Everything was mixed together in a bowl and spooned into place. I used the spoon to push the ore around to get an even coating. This was a little frustrating as the cork has little weight and offer no resistance. Patience and determination are of great benefit at this stage. it took several days for the load to dry. To finish I brushed a thick wash of dark and light grey stain over the load being careful not to hit the sides. An overnight of drying and final coat of matte sealer locked everything in place.
Since I am hauling silver ore in New Mexico a dark ruddy brown with black and gray grime is appropriate but any kind of rock ore could be modeled this way. Once the load is dry just stain it with whatever colors are appropriate. I have not tried this as coal but a careful base coat of black should be doable. Tape off the car top and finish with a coat of high gloss sealer to give the shine of anthracite or stick with the matte for bituminous.