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MODELLING SNOW


Snow

Snow is one of those very complex things that requires careful study before embarking on modelling.  Snow is actually precipitation in the form of ice crystals. These ice crystals are hexagonal prisms that form when snow freezes up. Prisms are formed due to the molecular structure of water. As these ice crystals are formed, they come down in one of the following forms:

  • Snow crystals -- Individual, single ice crystals, often with six-fold symmetrical shapes. These grow directly from condensing water vapour in the air, usually around a nucleus of dust or some other foreign material. Typical sizes range from microscopic to at most a few millimetres in diameter.

  • Snowflakes -- Collections of snow crystals, loosely bound together into a puff-ball. These can grow to large sizes (up to about 10 cm across in some cases) when the snow is especially wet and sticky. A snowflake consists of up to 100 snow crystals clumped together.

  • Rime -- Super cooled tiny water droplets (typically in a fog), that quickly freeze onto whatever they hit. An example of this is the small droplets of rime on large snow crystals.

  • Graupel -- Loose collections of frozen water droplets, sometimes called "soft hail."

  • Hail -- Large, solid chunks of ice.

Powder

Powder is freshly fallen, untouched, soft snow. Powder, tiny flakes and crystals form the smooth and soft surface in mountains.

Most snowboarders and skiers find powder the ultimate surface especially since it is the best snow to land on because it does not hurt as much as hard, compact snow.
 

Crud

Crud is the next phase from powder. As more and more people and traffic move through the powder, the snow gets piled at certain places and packed down at others. Fresh powder snow soon becomes "tracked out" and results in an uneven surface with lumps of soft powder-like snow and slippery patches

Crust


windblown snow crust

As the name implies, this type of snow has a harder crust on top of softer powder snow. Crust is formed when the sun's rays and the wind melt the top layer of powder, and then the cold air temperature makes it freeze into solid again.

Slush

When the air temperature becomes warmer than the freezing point, the snow starts to melt and its water content becomes very high. With this, the delicate snow crystals change into large grains of ice and slush is formed. Slush is basically snow that is starting to melt and thus becomes further wet.

Ice

This type of snow is the exact opposite of powder - hard and slippery. Actually, you'll never find real ice mountain and hill slopes. What you do encounter is snow that has been melted and frozen again for a number of times. This forms a solid surface of icy compact snow that is often referred to as "ice".

modelling snow

When modelling snow, it is essential to decide on what conditions you are trying for. Is it windblown powder snow which has drifted, conditions where snow still sticks to vertical surfaces or wetter snow that has fallen in large flakes? Has the snow begun to melt or is it still very cold?

The Bratton Fleming model aims at reproducing a fall from the previous night which is beginning to thaw.

As usual, reference to photographs is most important. Issues like how snow will fall from un-insulated roofs and how snow looks like after being swept or shovelled and walked on.

I find it essential to ensure that the 'snow' stays where it is intended as some of the materials used, (fine ground plastic or microballoon) can find itself in every mechanism you own.

materials

Woodland Scenics snow.

This comes in large containers and is a very good colour. The grain size is, however too large, but the material is good for building up layers. This I do using PVA painted accurately on to the surfaces where snow is required and then carefully sprinkling on the material. If the job is done over a clean sheet of paper, excess can be reused. The 'snowfall' can then be wetted using a mister with detergent added and the whole lot fixed by dropping on dilute PVA.


with the hip roof completed, the first coats of Woodland Scenics 'snow' is added

Microballoon is one of the best 'secret weapons' . This is 600 micron glass balloons and is used in the composite aircraft industry to mix with resins to produce lightweight filler. A good source in the UK is Europa Aircraft who will sell you 1/2 kilo (that is a lot) for about 9. A lot cheaper to buy it from here! This material is then sifted on to the wet Woodland Scenics snow. Detail can be added at this time using small soft brushed to push the 'snow' around, mimicking, for instance, slippage on a pitched roof.

If the microballoon become completely wetted with PVA it will dry more like slush ice and is an excellent way to model where people have walked through the snow.

Microballon can also be used for modelling frost with great effect.

The snow is then finished off using materials supplied by Deluxe Materials who supply a variety of different snow types which includes a very fine glitter which if used well will perfectly simulate sunlight reflecting on snow crystals.


the completed snow application using microballoon. - click on image to enlarge

Once the PVA has set, the snow can be fixed using artist's fixative. I must say however, that the result is delicate and cannot stand touching. Producing a realistic snow finish is not quick either. It took over four hours to treat the station building shown above.

Modelmates supply large aerosol cans of very realistic snow. This is about as good as it gets for trees, the direction and force of the spraying determining the snow finish required. The material does remain soft, so again, needs very careful handling.

Shake the can for at least one minute before use (and often while spraying). The can has to be warm to work effectively. A ball inside the can should rattle when the can is shaken. If the ball does not rattle, warm the can in your hands for about 5 minutes and then shake it vigorously. Keep doing this until you hear the ball and the can feels warm. The spray will come out very fast if the nozzle is fully depressed. As it hardens it will crack a little, just like real snow. When through spraying, invert can and spray for about one second to remove excess snow from nozzle. Should the nozzle become blocked, remove it, place it in boiling water for a few minutes and it will clear. Wash hands after use. To remove from smooth surfaces, first scrape off any areas of large build-up, then rub with a clean cloth (furniture polish also helps to remove snow).

The three main methods of application are:-

1) Even Application Of Snow:
Hold the can in an upright position approx. 300mm from the model. Press the nozzle very, very gently and fine snow will appear. Move the can across the model (or a part of the model) in one smooth motion.

2) Very Light Dusting Of Snow:
Hold the can in an upright position with the nozzle very close to the model, perhaps a tree or shrub. Press the nozzle very, very gently and fine snow will appear. Practise first before doing this. If you press gently enough only a very small amount of snow will be sprayed, just a light dusting.

3) Dense Application:
Hold the can in an upright position very close to the model. It important to press the nozzle gently at first, then gradually apply more pressure until you create the effect you are after. We make great snow drifts this way.

Alternately, simply point the nozzle as close or far from an object as you wish and press light or hard to achieve the effect you are after.

Never press the nozzle too hard - it comes out really fast.