The weathering of any rolling stock is unfortunately a dirty and messy job, when using chalks. The end results however, justify the little clean up afterwards. So here's how I do it.
You will need to obtain from your local Art shop the following coloured chalks. Black - Brown - Grey - Rust (light and dark) - White and yellow - Black Indian Ink.
Also required from a car accessory shop some windscreen washer fluid. Plus a can of Satin/Matte varnish from a hobby shop. This gives the final appearance to the finished article.
Once you have gathered all the items together, a start can be made on weathering that new looking rolling stock you have just bought. You will also need to find an old tin box or two (Old tobacco tins will do) or some plastic containers so you can scrape the chalks into them.
Before any weathering can be done however, a little cleaning with a soft brush is needed to get rid of any dust which might have settled on the rolling stock. Apart from anything else, the is only one rule to stick to. - Light coloured cars need dark chalks - Dark coloured cars need light chalks.
The ink wash
The first thing on the agenda is to spray the car with the Satin/Matte varnish, this will give the chalks something to grab hold of if you like. Take it outdoors to do it. Once the car has dried (approximately 2 hours) a start can be made to make you car look like it's been in service for years. With the Indian ink, grab an egg cup (Make sure the wife's not looking) and put about four drops into the bottom of the egg cup. Now, with the windscreen washer fluid, place about a soup spoon full into the egg cup and mix it all together. An old brush will do or some soft brush or other to flow the liquid onto the roof and sides of the car. It will run everywhere, but that is exactly what you want it to do. Just keep on stroking the brush down the sides of the car until the effect you require has been achieved. Flow more on the roof from the middle out. Now with a paper towel, dry the brush off and start to wipe off the wash in the same direction you put it on. Once all this has been accomplished, leave it to one side to dry. As it dries, the dark colour of the ink wash will highlight the raised details. (Rivets etc.)
Right, lets assume that the car has dried, and proceed onto the next stage with the chalks. As I stated earlier, light chalks for dark cars and dark chalks for light cars. So, which ever car you have started needs the appropriate chalk colours. Let's assume your car is darkish yellow, now, it should with the after effects of the ink wash look a little older already so now subtle chalk weathering is needed.
Scrape some chalks into those tin boxes I asked you to get, or some plastic containers. I would expect with a dark yellow car that red rust and a little grey and white will be all that is needed for this car. With the shaving brush (Now dry) dip it into the rust chalk and brush lightly over the car trucks and couplers. Use a very small amount of grey and white brushing from the top of the car down in a straight line. This will leave a streaky effect, and is what you are after. When all is done, turn your attention back to the trucks and couplers. Grind up a little rust into the bottom of the egg cup and with a small paint brush dipped into water ,then into the rust, brush over the trucks again. Brush on a little at a time, if you get too much on, use a paper towel to take it off.
All that is left to be done to the car after all the chalks have been applied is to take it out doors and spray it again with the Satin/Matte varnish, this will seal the weathering for ever.
There are of course other ways to weather your rolling stock, some people like to use an air brush. I new one person who actually left a loco body shell outside in an empty bucket for many months to try and achieve a natural look, but I don't think it worked well.
Rusting with liquid rust.
This bottled "Magic" is bought from :-