The principle applies to all the smaller scales simply use what looks good to you.
1/ It's readily available.
2/ Usually obtained free
A tray of Pine Dust ready to sift.
Start with the strainer with the largest mesh. Half fill it with your raw dust and while holding over a container start stirring. When saw dust no longer falls through, tip remainder into another container. The largest shavings are ready for colour. Now start on the next size strainer down. This is repeated with successively smaller strainers until you have enough.
If you have lots of curly shavings these can be reduced in a blender very easily.
Half fill the blender with water then turn it on and add several handfuls of the sawdust and blend until your happy with it. Warning
Kids ask Dad first.
Guys wait until your wife's out for the day, be very careful to get it clean afterwards.
Spread it out on an old T-shirt or such and leave to dry 24 hours then stir it with your fingers & leave it until it's dry.
Tools you will need.
1/ Mixing pot similar to this 1.5litre one of mine.
2/ Assortment of kitchen strainers. I use 4 different wire mesh sizes.
3/ Trays or containers to catch sifted dust.
4/ Paint stirrer, wooden spoons etc. for mixing.
5/ Plenty of dry rags.
6/ Area to spread wet coloured saw dust to dry.
7/ Stirrers for stirring the sawdust whilst sifting.
8/ If using Stains, Dies or Paints that require thinners, appropriate thinners will be needed. In the case of enamels and Auto Acrylics a cheap general purpose thinner will do.
9/ If using thinner based paint a well ventilated area to work in.
10/ And finally a good supply of Sawdust. ( make some phonecalls, look around. You shouldn't have any trouble getting 3-6 different coloured sawdusts.)
The shape of the Sawdust is largely determined by the type of Saw blade used and whether cross cut or ripped length wise.
Cross cut will give the particles we require in larger quantities.
Rip sawing will give the curly bits (Great for foliage in larger scales)
Sources of Sawdust
Every town or suburb has a Cabinet maker, Kitchen maker or even a Furniture maker, If you're young enough to be still at school and your school has a wood work shop ask your teacher if you can collect some sawdust. Most of the buisinesses have to pay to have waste taken away & will gladly let you have a few bags full.
The larger the shop the more likely they have saws set up for particular wood types therefore producing different colours of sawdust for each saw. If you can source these different colours it adds to the variety of foliage colours you produce.
I have access to sawdust from various coloured timbers from my neighbour and I had/have on hand numerous different colouring mediums, ie: Leather dies, wood stains and numerous paints, in enamel, water acrylic, auto paints in enamel and acrylics, Tyre black & kids art paints.
Anything with colour is usable.
After my first batches were dry I sifted into particle sizes. I found some of the larger partiles would never be used, as these colours were more for flowers on the trees rather than overall foliage colours: these being yellow, maroon, pink etc. These smaller particles are suitable for flowers on trees & shrubs.
The first decision is.
1/ What is the largest particle size I need ?
2/ And how many colours will I need in that size ?
Put about 1/2 an inch of paint in your mixing bowl & thin to consistancy of water.
Add the sawdust and stir keep adding sawdust until it stops colouring- you'll see raw sawdust mixed through the colour. Don't attempt to add more colour. Left like this it adds reasism to the mix.
Now lay out some rags and spread the mix out evenly on it & leave 24hrs. Then stir it with your fingers and leave it until dry or free of paint smell.
Any lumps can easily be crushed between fingers, or put aside for Rocks if the right colour.
A sample of colours & particle sizes.
Now It's all dry you are ready to SCENIC. Bear in mind no two trees or patches of grass are exactly the same colour, so keep adding bits of colour to your mix as you progress.
In this next picture ALL the Scenic material except the road surface (which is marble dust from a stone masons saw) is coloured sawdust. Look carefully at the colour mixes. They are based on every day colours in Australia. Simply make your mix fit the area you're modelling ( a little research adds a new dimension to the modelling fun).