How it all began.
Out of the box, couplings removed but no hoses yet added to the buffer beam.
High-tech cradle in use to support upside down model while underparts are dirtied. The battery is used to turn the wheels during airbrushing, to avoid paintless shadows from the connecting rods and to get to those parts of the wheels hidden behind the frames.
For this project I have chosen to use Railmatch Frame Dirt on the underparts. This is not my usual colour for working on underframes, but I had some available so thought I'd give it a go. The airbrush I am using in this case is an Iwata HP SB Plus, because it gives me a great deal of control over the area to be covered for each pass along the model.
When working on the whole length of a model, whether it is the chassis, bodysides or the roof, I like to have complete control over the area to be covered rather than just blasting away and then cleaning up afterwards. The two main ways of achieving this control are masking and distance from the subject. In this case I'll be carefully positioning the airbrush before pressing the trigger to ensure I only cover the wheels, brake gear and, probably, the lower edges of the frames.
I won't be doing any masking.
Getting tools prepared. As already mentioned, the airbrush to be used is an Iwata HP SB Plus, with a 0.2mm nozzle for fine control when working close up. I'll be utilising this airbrush's ability to come in close and only cover small areas at a time.
The glass dish contains clean white spirit, as does the plastic bottle to the left. The former is used during the mixing of paint to achieve the necessary consistency and the latter will be used to keep the internals of the airbrush clean during the spraying session.
The first few coats of paint have been applied. Each coat consists of a pass across the chassis to apply a very light coat of paint. This only results in a very slight discolouration of the wheels, or at least those parts of the wheels that show above the frames. The wheels are then turned a quarter of a turn using the battery and the exercise is repeated.
You can see in the accompanying picture that there is still one small area on each wheel that needs to be covered. You can also see that although there has been some overspray, it is only covering those areas that would be as dirty as the wheels. Notice also that the turning of the wheels while the paint is still wet has kept the pickup-wiped rear surfaces of the wheels clear of paint. No attempt has been made to keep paint off the wheel treads.
Round to the other side of the chassis now. Same process, but you can see where the last rotation of the wheel has yet to be sprayed. Still no masking, and the small spray area resulting from coming up close has kept the overspray off of most of the frames. Turning the wheels with the battery is still keeping the backs of the wheels clear because the wiping action of the pickups is removing the still wet paint.
Clean wheels.
With the aforementioned battery applied to a pair of wheels, a cotton bud soaked in isopropyl alcohol has been applied to the wheel treads and the backs of the wheels. You should be able to see that all of the dried enamel paint has been completely removed from those surfaces that need to be clean for conducting electricity. Isopropyl alcohol will remove all enamel and acrylic paints from these surfaces, so you will need to take care with where you apply it.
The frame dirt has now been airbrushed onto the frames as well, taking some care not to get overspray onto the body. This is not critical, but it helps to keep extra work to a minimum if I decide to spray the bodywork a significantly different shade of filth. With the locomotive upside down in the cradle, it is quite easy to ensure that the underneath of the running plate is covered. The accuracy of the airbrush also helps to keep unwanted paint off the wheel treads.
The locomotive has been removed from the cradle and further light coats of frame dirt applied. The next task is to spray from above the chassis components to cover areas inevitably missed while it was upside down - particularly the steps, axleboxes and sandboxes. There is some overspray, but that will all help to make the bodysides and running plate look grimy once the next steps are completed . . . . . .
Buffer beams get very dirty, even on slow moving stock, so this needs to be portrayed on a model for it to look right. This build-up of grime is portrayed by several coats of (in this case) frame dirt, added a little at a time and manipulated before it gets too dry. These photographs show the first coat to be applied - just a thin application that barely shows up.
The next step is to randomly remove some of the paint to portray a buildup of grime around things like coupling hook, bolt heads and pipe connectors. This is achieved by using a slightly damp brush, and by that I mean a couple of drops of thinner placed on the bristles rather than dipping the brush into the thinners. The brush is then used in a stabbing motion, rather than a stroking motion, to slowly and gently remove the paint. If it all comes off straight away, your brush is too wet!
Another method is to use a cotton swab that is damp and perform the same actions, although this will inevitably leave some cotton strands about, and you'll forget to blow them off before taking a photograph . . . . . . .
There is a great level of detail on the body of this model, and it will look even better if it can be highlighted in some way. This applies to pretty much all of the ready to run rolling stock available these days.
My plan for this shunter is to use a panel line wash applied to all the crooks and nannies with a rigger brush. What's a rigger brush? It has long bristles and a small point - some folks call it a lining brush. The idea behind using this type of brush is that the bristles hold plenty of paint, but the small tip allows it to be applied with a degree of precision.
The wash I am using is Ammo by Mig Black Night, but you can use any dark colour to achieve the effect. The process involves dipping the brush into clean thinners (in this case white spirit), dipping the brush into the wash and removing the excess (the blob on the tip of the brush). The tip of the brush is then touched to the corner of a panel or edge of a door/window moulding, and capillary action takes the wash along the detail. Easier to do than describe!
Once all of the panel line wash has been applied and allowed to dry completely (24 hours), it's time to start airbrush work on the body. Using the same Railmatch frame dirt as before, but mixing it with a little Railmatch weathered black, a very light misting is applied to the whole locomotive. Side, ends, top and underparts. This is deliberately not perfectly even, more being applied in some places than in others, because I don't want the end result to look as if it has had a perfectly even coat of paint airbrushed onto it.
You can see by looking at the roof in particular, that this process has added a dusty texture to the paintwork. Care has to be taken not to overdo this in 4mm work and below, but from 7mm upwards it becomes more necessary.
The airbrush has been loaded with a small quantity of AK Interactive Engine Oil in order to replicate the oily residue at the bottom of the filters. I have masked off the underframe while doing the filter area, just a piece of card laid against the running plate. Only a very small area has been thus affected on this particular locomotive.
The areas around the axle boxes are to be portrayed as oily and affected by accumulated gunge. The beginnings of this process incorporate a layer of Railmatch Weathered Black. This is applied thinly and from fairly close up, to control the area covered. Overspray onto the running plate is deliberately not avoided. In this photograph you should be able to see the result of applying the small amount of engine oil to the base of the bodyside filters.
If you ever handle thinners inside the spray booth, make sure that your latest project is not in there as well!
Lack of control of Bonwick fingers have resulted in a large blob of thinners landing on the roof. To deal with this, the section of roof has been cleaned so that I can start again.
I said at the beginning of this, there would be bad things as well as good things reported!
The roof has been fixed. Not quite the same shade of dirt as the rest of the roof, but that is not a problem, because another layer will be applied at a later stage to tie it all together.
This view of the other side shows up the effects of darkening areas affected by oily spillage (around axleboxes) and not controlling overspray to simulate dirt accumulation (areas just above the running plate).
The main work has been done, and the airbrush can be set aside for a few steps.
Weathering powders, or pigments as I tend to call them, come in a great variety of textures and colours. The ones that work best for me are from military modelling ranges and are exceedingly finely ground. This enables the particles to fall into the lower reaches of the matt surface's layer(s) and stay there beyond the reach of fingers and other abrasive effects. In this case I'm using MIG Productions colours Dark Mud (for new rust), Track Brown (for old rust) and Black Smoke (for accumulated oil and grease).
I apply the pigment using a filbert brush, and collect the finest particles I can from the lid of the jar. The excess is removed by tapping the brush on the edge of the jar and the pigment is applied by gently touching the bristles to the target surface. The result will be a barely perceptible discolouration of the surface, and more intensity can be achieved by repeating the process.
The reasons for the choice of brush are that it is designed for use with acrylics, so will be pretty tough, the bristles are fairly soft but quite firm and it is a pretty shade of yellow. 
You will note from the photograph that the bristles have lost their shape, but it has been in use for some 5 or so years.
Pigments have been used to simulate the rusty surface of the exhaust silencer assembly.
The technique is to pick up pigment particles from the lid of the pot rather than plunge the brush into the pot itself. This means that the finest particles are being used to apply to the subject. The brush used is a filbert, chosen for its soft but firm bristles and rounded shape. I like soft, firm and rounded. Only small quantities are used, because it is only a suggestion of rust, and not a flaking, encrusted pile.
I felt that more discolouration was needed around the bodyside filters and the axle box areas. More pigment has been applied to these areas to achieve this, and the same method used as before.
MIG Productions pigments (shown in this blog) are now out of production, but the same colours are available from Abteilung 502 in the same shaped pots but with different labels.
The oily locations need to be made oily.
I have used AK Interactive Fresh Engine Oil through the airbrush to add the oily shine to appropriate areas - axle boxes, bodyside filters and chassis areas. The photograph shows the application while still wet - it will lose some of the shine by the time it dries.
To increase the level of accumulated dirt around the bodyside doors, some more pigment (MIG Productions Black Smoke) has been added with the filbert brush. By using small quantities again, the effect has been kept to a minimum. A little has been dragged downwards from the cab window and from the sloping top of the fuel tank. The cab roof has been treated and so has the area around the bottom of the oil filters. In all cases it has been just enough to disturb the even surface produced by using the airbrush.
Similar treatment has been given to the other side, and you might just be able to see where the same pigment has been applied to the cab end.
I thought that the shine from the oily finish under the running plate was a bit too bright, so it has been dulled down a little with some dark brown pigment. This was applied in small quantities (heard that before?) with a soft brush.
I think I'll finish this subject right here. Resist the temptation to fiddle!
There follows a summary of materials used in this project with the step numbers where they appeared.
- Railmatch Frame Dirt - Step 3.
- AMMO by Mig Panel Line Wash Black Night - Step 12.
- Railmatch Weathered Black - Steps 13 and 15.
- AK Interactive Fresh Engine Oil - Steps 14 and 21.
- MIG Productions Dark Mud - Step 18.
- MIG Productions Track Brown - Step 18.
- MIG Productions Black Smoke - Steps 18 and 22.
There is another photograph of the (almost) finished locomotive in my flickr photostream at:
https://www.flickr.com/photos/laughinglobster/43570994831/in/dateposted/
The techniques, tools and materials used in this project can be used for many different weathering tasks. If there are any queries about anything shown here, then don't hesitate to ask.