Sunday, 25 January 2015

Revell 1/144 P-47 Republic Thunderbolt - Pt. 3

[Sub-title: Plasti-Kote experiment No. 2]

Well, here we are, part three of my Plasti-kote P-47 experiment. And despite the disappointment that my Plasti-kote bright metal finish failed to materialise in the hoped for quality I plod on as there are still a few things to learn about this paint.

This time I am looking at masking and how coats of paint applied on top of the Plasti-kote

I was a little worried about masking the Plasti-kote bright metallic as it seemed susceptible to marking and in my first experiment with the toy plane it actually peeled off when I removed the masking tape. However, I am fairly confident that was something to do with the cheap greasy plastic of the toy and won't happen with paint applied to good quality plastic.

But just in case I used as little masking tape as I could and also used my best quality Tamiya modelling masking tape, which is low-tack.

As usual I use proper masking tape for the actual masking and protect all other
areas with cling-film. The cling-film also helps protects the already painted areas.
I did have a bit of indecision about whether to mask all non-silver areas before spraying the Plasti-kote. My thinking was that as the Plasti-kote is a gloss that I might be better leaving the black primer exposed for the other paint sections - like the red engine cowl and tail - as I wasn't sure how well water-based acrylics would take to the Plasti-kote. But my initial experiment with the toy plane seemed to belay my fears and show that with care acrylics could be used onto of the bright metallic.

Humbrol spray paints have no problem with the Plasti-kote, but air-brushing on acrylics has to be done with some care. You have to get you paint to thinners mix right - in the case of my Vallejo Model Color acrylics this meant I had to add as little water to the mix as I could.

Too much water caused the paint to bead on the surface of the Plasti-kote gloss. The 'neater' the paint mix the better it adhered to the gloss when sprayed onto it. Even so I still had to do the spaying in stages - first spraying a a very thing neat mix lightly to create a base for further light coats. In this way I built up my paint coat onto the Plasti-kote to the desired consistency.

In fact I used the Vallejo Model Colour with only one or two drops of water - just so it would go through my air-brush without choking or splattering. I didn't try Vallejo Model Air paint - which is pre-thinned for airbrushing so can't say how that would fair.

The good news was - with much relief - that when I removed the masking take none of the Plasti-kote paint layer peeled off. There was, however, a little discolouration and marking here and there due to the masking tape gum. This looked like small smudges and dulled the bright metallic shine and could not be 'polished' up again - though I didn't want to rub the Plasti-kote too aggressively.

Experiment over!
Drat! It's a big fat 'fail' for Plasti-kote Bright Metallic I'm afraid (it fell at the final hurdel)!

Plasti-kote Bright Metallic paint does not like cling-film!
Just when I thought I was going to pull something marginally positive out of this experiment and Plasti-kote turned around and bit me in the ass. Basically the peeling I mentioned that occurred with the first experiment I did was NOT a fluke caused by the cheap plastic of the model I used. Plasti-kote peels big time no matter what preparation...

My guess is that smooth plastic is not a medium that Plasti-kote's Bright Metallic is compatible with. Looking at the Plasti-kote web site it gives a list of materials you can use this paint with and they all appear to be - to one degree or other - porous. The Bright Metallic seems to need a slightly textured surface to adhere to properly.

Of all things it was the kitchen cling-film that caused the peeling you see in the above picture. The sticky plastic seems to have some sort of chemical reaction with the Plasti-kote and despite cling-film not being all that sticky it lifts the metallic paint up like it was designed specifically to do just that!

A beginner's mistake - trying to spray over another coat of Plati-kote in the vain
hope it would cover up the flaked paintwork showed why multiple coats of this
paint are not a good idea! Still, the area where the masking tape took off the red
engine cover paint looks a nice effect! LOL
I'm gutted in a way as it has completely spoiled the model - I suppose I could try cleaning the paint off the wing but as I have found out what I wanted to about the plaintive unsuitability of Plasti-kote's Bright Metallic spray as a modelling medium I hardly feel I want to. It would just be a bodge-up job at best. (But I may feel different once I have slept on it.)

Elsewhere, the masking tape also lifted some flecks of the metallic paint and otherwise discoloured other areas. It was like Plasti-kote was just bidding it's time waiting to show it's flaws right at the last minute!

This seems a lot of work just to find out what others have already said, that Plasti-kote Bright Metallic paint is not for serious modellers. But at least now I know exactly why (and you do to).

Next: Not sure if there will be a next - at least it was just one Pound (£) I wasted! May do a de-brief of what I think of the Revell Micro-Wings P-47 though.

Revell 1/144 P-47 Republic Thunderbolt - Pt. 2

[Sub-title: Plasti-Kote experiment No. 2]

Right, it's crunch time...

But before I get to the nerve-wracking Plasti-kote spraying I have to lay down the primer coat. I'm sticking with Halford's enamel car touch up spray, I think it does a satisfactory job (I haven't tried a specialist primer which you apply with an airbrush yet, I'll use up the last of the Halford's first).

Black does look nice doesn't it? (Note to myself: Must do a night fighter at some point! Airfix has just released a new tooling of it's 1/72 Boulton Paul Defiant. Hmmmm...)

Anyway, one little quandary was the canopy. As mentioned in the initial post, there is no pilot or cockpit detail and as I want this model 'in flight' I am going to disguise this fact by painting a faux-canopy (in war-game fashion). Not having done this before I wasn't sure at what point to affix the canopy to the plane - thinking about it now I wish I had attached it before priming so that it was a flush and integral component. Ah, well - you live and learn!

The Plasti-kote coat! (Du-du-duuuuh!)
Now, one thing - I'm having a right kerfuffle photographing 'chrome' finished. I really should set ip my mini-studio lighting, but I can't be bothered raking through our attic to find them. So, the following photos are a little hit and miss.

Well, here we go...Fingers crossed...

First, a bit darker (high flash) to bring out the reflections...
And then lighter to show the texture.
Now, I'm a little disappointed and mildly pleased at the same time (but more disappointed).

In my first test I mentioned that I thought that the best way to achive a smooth, high reflection finish with Plasti-kote Brilliant metalic was to spray one, fast pass and hope for the best coverage (just touching up any small imperfections and spotty coverage with a light focused spray). This time however - as this is all about experimentation - I decided to gamble and follow Plasti-kote's own suggestions about a second coat (thereby ensuring total coverage).

I had read that additional spray coats with this sort of bright metallic paint resulted in subsequently duller finishes. This seems to be true - although the 2-coat finish isn't all that bad, it's not 'chrome' but rather what I would call 'polished steel'.

Actually, there is rather a nice effect if you look close - it is like a machine polished surface...

If I were doing a 1/72 model of Lindbergh's 'Spirit of St. Louis' this might be a nice effect!
But...There is also a less desirable 'speckling'. And remember, you cannot 'smooth out' this unwanted texture by adding a gloss varnish - you cannot varnish Plasti-kote Bright Metallic.

Obviously, at a distance the finish looks acceptable, certainly for a war-game modeller who might simply want the look of high-polish quickly. But for the (ambitious) display modeller this quality of finish would be totally unacceptable.

In short, my 'one pass' theory is probably correct - but trying to get a good coverage with just one coat is, as I mentioned after experiment No. 1, down to pure luck (which isn't what you really want to rely on as a modeller).

OK. I'll put this one down as a 'fail'. Maybe a bit harsh and not a total loss as this was an experiment after all, but the texture just doesn't work for me I'm afraid.

Looking back at my Hobby Boss Mig-15 - which I did with just normal Humbrol acrylic silver spray - I think I preferred the duller but smoother silver finish...

Amusingly - re-reading my Mig-15 blog post - I do mention that I didn't enjoy working with a silver finish. Little has changed it seems.

But, I think my mind is made up that if I do want a professional looking high reflection and smooth finish and it's a display model it really is worth going the extra yard and using one of the specialist modelling metal finish mediums, like Alcad. Horses for courses.

At a distance look...At this distance the spotty texture isn't as obvious. But it's still there!
What next?
Well, naturally, I want to finish the P-47 model off, and there are still some things to learn about Plasti-kote - like how does it handle masking?

So, in the third and final part of this experiment I will adding the remaining areas of colour, the canopy and the decals.

Saturday, 24 January 2015

Revell 1/144 P-47 Republic Thunderbolt - Pt. 1

[Sub-title: Plasti-Kote experiment No. 2]

My initial experiments with Plasti-kote's Brilliant Metallic spray paint convinced me there was a certain merit to the paint. Unfortunately the subject that I used for the tests was a rather cheap and nasty toy plane, the surfaces of which prevented me from getting a clear idea about just how smooth the Plasti-kote could be applied. So I decided a second test was warranted.

I wanted to use a proper injection-moulded plastic kit as the guinea pig this time, but - of course - still didn't want to go to the bother and expense of using one with which I has some sort of emotional or financial investment. I wanted something cheap and cheerful that I wouldn't be too concerned about if something went wrong.

Not the scheme included in the Revell kit instructions I'm afraid, but the only colour reference
I could find of a P-47 of the US 9th Air Force. Picture source: Wings Pallette.
As it happens a local store was selling an enormous pile of Revell Micro-Wings models - an over-stock I presume - at the knock down price of just £1 a piece. And although these are diminutive 1/144 scale aircraft I reckoned they would be simple, quick and easy test beds for painting practise.

I picked out one particular model which had a bare-metal scheme, the Republic P-47 Thunderbolt or 'Jug' as it was nicknamed by it's pilots. (Not a mirror-finish, I know, but it was the closest they did.)

The Revell 'Micro-Wings' 1/144 scale P-47 Thunderbolt
I enjoyed making the two 'micro-scale' scale aircraft I have done already - an Eduard Me109 and a Tamiya IL-28 Beagle - so I was curious to see just what kind of quality the Revell 'Micro-Wings' kits could be. To be honest, for a quid I wasn't expecting much!

Left: The contents of the 1/144 Revell P-47 kit. Just one main sprue with 16 parts. Not a complex build then! Picture credit: (As I forgot to take a snap of before I cracked on with construction!)

I believe these mini-kits are aimed at the younger modeller/collector as they are quite simplified. The exterior detail is cursory and there is no interior detail at all - no cockpit, no seat and no pilot. Still that was ideal for my purposes, simpler the better.

By default Revell guides you towards building the aircraft with the undercarriage down and yet supplies you with an ‘in flight’ stand. I wanted to model this fighter ‘in flight’ so the stand is handy but that does mean you will have to modify the under-carriage (more on that later).

And that is all there is to it!
A related issue, which bears considering before you jump into the build, is the lack of a pilot. Again, if you decide to build the aircraft ‘in flight’ the absence of a pilot will look a little strange. Therefore, you will have to decide whether to make your own tiny pilot (a pain) or paint the canopy so that it is not transparent. Some like a ‘display canopy’ (a painted windscreen) and it is a convention in war-gaming and as this has no impact on the purpose of the kit for me I decided to paint mine.

There is just one set of decals and one associated colour scheme (printed on the front of the box). The monochrome printed instructions advise you on the specifics of this scheme and decal layout. Again, this is sort of irrelevant to me as this will be a quick build and I’m not bothered about representing a specific type or unit.

P-47D-30-RA, “3T-H”, 22nd Fighter Squadron - 36th Fighter Group, 9th US Air Force, 1944
Construction - the nitty (and very) gritty
I could tell - even while still on the sprue - that the quality of the moulding was ‘vague’. There was some flash and - unfortunately - a few ‘sink holes’ generated by the moulding process. I immediately acknowledged - much to my chagrin - that there would have to be some filling.

I know this is just an experimental project and build quality is of secondary importance, but I just can’t bring myself to bodge together a rickety and sloppy model.

The dirty fuselage is a result of spraying the interior black, in case I use the canopy as is.
Anyway, on with the building. Fuselage and wing sections needed clamping to encourage a successfully mating of the various halves, but there was a tiny bit of overlap on either sets of components. Nothing some sanding couldn’t rectify but on the fuselage the central seam would need some filling and sanding to try and produce a seamless join.

The next glaring fit related issue was when I moved on to join the wing section to the fuselage. There was a obvious gap at the wing roots and underneath which would also need some filler putty. (I kept reminding myself that this was suppose to be a ‘quick build’!)

However, there are not many external parts, just a couple of bombs and a central drop tank and they are all one-piece components. But, unfortunately the flimsy .50 cal machine-guns became a victim of my rough treatment and very soon broke off, so I quickly replaced them by drilling some holes and popping in some replacement brass rods.

The next major issue was - as noted before - the fact that I wanted the undercarriage up. I first of all tried fitting the supplied landing gear and gear doors in the ‘up’ position but found the fit left a lot to be desired…

I managed to make the gear doors fit (after a little filling) but the landing gear had to be scrapped and instead I filled the vacant holes with some Milliput putty, fashioned roughly into shape. Once completely dry I would sand these rudimentary landing gear covers flush with the wings.

Finally, there was the fitting of the distinctive engine cowl. This big oval cover, sadly, suffered from some sink holes on either side which had to be filled and smoothed out. 

I decided to fit this in place and paint it BEFORE fitting the prop (the instructions suggest fitting the prop to the cowl and fixing it in place by gluing on a plastic collar so that the prop would spin freely). I don’t mind the prop not spinning and it would make painting the engine and prop easier if I fit this after fitting the cowl.

At this point - were I a rivet-counting aircraft geek - I would point out the very shoddy job that has been done with the shape of the prop. It was also sightly deformed, but there again am I bothered? 

So, that was the major construction completed and the various ill-fitting seams and sink holes filled and sanded…

Now, onto the actual painting and the scary Plasti-kote application…Gulp!

See you in part 2 of this post (or if it never appears you will know that the Plasti-kote spraying was a disaster!)


Friday, 23 January 2015

Plasti-kote 'Brilliant Metallic' spray experiment

Photo credit: Matthias Dorst - The Warbird Information Exchange. And no, I
do not think they used Plasti-kote on this beautiful P-51!
I'm a great believer that you don't really know about modelling techniques until you try them yourself. While there are a great many comments on model forums about this and that technique and a great many example photos you never really quite know the full process that these modellers undertook to get that final shot or opinion. Plus - importantly - a lot of modellers are a bit shy about showing off their failures, which of course teach you as much about a technique as do the successes.

Thus, I am undertaking a test of a fairly well documented medium because I need to see - close up - exactly what Plasti-Kote 'Brilliant Metallic' spray paint does (or doesn't) do.

I am interested in this paint as it's very readily available and - unlike many proprietary specialist modelling chrome solutions - is comparatively cheap. I don't profess this would be an expert modellers choice but rather a possible 'quick effect' for war-gamers. But before we talk about using Plasti-kote on models lets get an idea what the product is actually intended for...

Platsti-kote 'Brilliant Metallic' spray is not - apparently - just another metallic-effect paint but, to quote Plasti-kote themselves: "This specially formulated paint is made from tiny metallic particles which are highly reflective."

What this means in practical terms is the paint produces a highly polished and near mirror effect, rather like chrome. For modelling this would - in theory - be really useful for models like aircraft with bare metal or polished aluminium surfaces (like some WW2 fighters and post-war jets). Obviously this is NOT what Plasti-kote was intended for - so bear that in mind.

I did some research about it's use for modelling but information was sparse, it seemed, and what there was was not very encouraging. The consensus being that this product was not a suitable medium for the serious modeller. Well, never let it be said that I am a serious modeller!

Undercoating for metallic sprays
There was a general view that if you are going to use these sort of 'general craft' or DIY metallic spray paint for modelling then you should lay down a good quality black enamel coat first.

I decided I needed a low-cost expendable guinea pig to try the Plasti-kote on and so delved into my 'scrap toy box' and came out with a horrible plastic aeroplane which I got in a bag'o'soldiers from the local Pound store!

My undercoat was a layer of good old Hallford's black car touch up spray paint. I went for matt though there are some who suggest gloss - I think it is a matter of personal preference. As usual this went on very nicely and did not noticeably eliminate any of the detail - such as it was - on the toy plane.

Why black? I'm not entirely sure, but I think it has something to do with creating a 'mirror effect' where it enhances the reflective properties of the metallic top coat...Maybe?

Working with Plasti-kote 'Brilliant Metallic'
I didn't have high hopes for the quality of spray from a can - by that I mean that I suspected that the paint molecules would be big and spat out in a dense cloud that could easily lead to over-spray. So I tried to off-set this danger by doing very quick light passes with the spray can, and this seems to have worked...

No...Before you say anything, I didn't bother to tidy up seams or clean off flash!

There is an element of luck in this as the idea is to get one light coat with perfect coverage in one go! I am told that over-spraying is not a good idea as the thicker the coat or the more coats you add the duller the paint effect becomes. Although Platsi-Kote says: "Allow to dry for 10 minutes between coats. Touch dry in 10 minutes. Thoroughly dry in 2 hours."

In my opinion, less is definitely more in this case. Although I did have to re-spray two isolated areas where my coverage had been poor and it didn't seem to have all that much of a detrimental effect.

Working on-top of Plasti-kote
Now, all very well and good...Much to my surprise, I now have an attractive 'mirror finish' coat. Coverage was quite good - as it was a new can there was no splatter - and smoothness of coat was OK (though to be fair the quality of the toy plane's surface was less than perfect).

In effect the Brilliant Metallic is a gloss paint, which has some implications if you intend to work over this surface.

Trying to brush paint matt acrylics onto this glossy surface is a bit of a bugger, enamels would fair better I suspect but the best way to cope with it is to spray any further colour areas on. I tried out some patches of colour using Humbrol acrylic spray can paints and a couple of thin coats worked well.

I did the orange stripe around the fuselage with Vallejo acrylic using the airbrush
and despite the Plasti-kote being high-shine gloss it actually went on very nicely. 
The good news is that - because the Plasi-kote is glossy - decaling is a breeze. No need to prep the surface by laying down a gloss varnish...

Again I consulted what internet references I could find and the general view seems to be that decals can be applied directly onto the Plasti-kote and similar bright metallics as they are already - effectively - gloss coats. The decals took to the surface quite well and with no silvering, and I used some micro sol just to aid the decal settle into the panel lines. BUT...

Unless you paint some sort of varnish directly onto the decal - carefully avoiding the Plasti-kote - you should avoid sealing the decal for the following reasons...

Sealing Plasti-kote painted modelsThere is always a 'but' somewhere in anything you do, and sure enough here comes the 'but'!

Finishing off the model you have painted using Plasti-kote Brilliant Metallic poses something of a quandary. Usually I would finalise my model by sealing the whole thing with a thin coat of satin or matt varnish...YOU CANNOT VARNISH PLASTI-KOTE BRILLIANT METALLIC!

Plasti-kote warn: "If a sealer is applied over the top it will stop the particles from reflecting in the light and the paint will appear duller."

I did an experiment and sure enough...

Vanished area on the left wing...Which is on the right!
I masked off slightly more than half the plane leaving the left wing and tail exposed. I then sprayed on a light coat of Humbrol's Acrylic Gloss Varnish, the result was immediate and obvious. The varnished surface lost it's lustrous mirror effect and became dull and flat.

So I did some more intensive web research on the issue and found a couple of articles where the authors suggest that if you do use a mirror effect paint like this then you should leave your model unsealed. This means you will have to decide what to do about any additional painted surfaces you apply over the Plasti-kote and consider how to deal with decals.

Incidentally, I tried out hand-brushing a small area with Pledge Klear - which happens to be a very nice crystal clear varnish - instead of spraying on a specialist acrylic varnish. The result was little better that the Humbrol lacquer and the Klear tended to pool more resulting in unsightly dull blotches all over.

Conclusion - the pros and cons
OK, well this did go a bit better than I expected. The bottom line is that IF you do want a mirror finish on a model BUT don't want to spend a lot of cash and time on advanced modelling mediums OR have a lot of models to do quickly then MAYBE Plasti-kote Brilliant Metallic spray paint is an option.

That said, there is no doubt that - for display modellers - that there will be too many down sides for this to be considered an ideal solution. The quality of the coating from a mere 'rattle can' could never be as good as a proprietary effects paint delivered from a fine airbrush. The thickness of the coating and the unpredictability of the coverage makes the whole thing unviable.

In the end the product is what it is and trying to make it do something it was never intended to do was alway likely to end in one way. It's a no-brainer really. BUT for the war-game modeller there is some use to be derived from this paint, particularly if you are doing a number of the same type of model and time is an issue. As long as you are aware of the issues connected with working with this sort of product then you will not be surprised by any of it's accompanying quirks.

And finally, how to do 'chrome' properly?
You will, of course, make your own mind up on how successful or appropriate Plasti-Kote is as a bright metallic medium, but here are a couple of links to show you how expert modellers tackle this tricky finish...

Link to Plasti-kote (UK) 'Brilliant Metallic' product page

Thursday, 22 January 2015

Featured work - Zvezda's new 1/72 IS-2 tank

Zvezda's new 1/72 IS-2, made and painted by Denis Kurov.
I do like Soviet heavy armour - though I can't say exactly why (maybe it's because there's something malevolent, course and almost robotic about them, like they are an alien iron species). Anyhoo, flights of fantasy aside, they are superbly monstrous mountains of metal.

Zvezda is gaining a really impressive reputation for display quality kits - I bought their T-34 and it was very nice indeed, if a little expensive - and this series of publicity photos really does show off their IS-2 very well. It was made by Denis Kurov.

Link to Zvezda website (English):

Link to Zvezda on Facebook

Friday, 16 January 2015

Track weathering experiment No. 3

I've had a few goes at painting model tank tracks and generally I've been quite pleased with my hap-hazard techniques. But now I want to try and find a formula for painting tracks in a consistent manner, so I looked around and found a few possible techniques in order to develop my own 'recipe'.

Probably the happiest I've been with a set of tracks that I've weathered was the
set I did for my 1/72 Pegasus KV-2. This was within the 'Goldilocks' range of
weathering - in my opinion - being not too much or too little mud and rust.
Unfortunately, I didn't keep a note of what I did - hence this experiment! Du-oh!
As the title suggests this is my third attempt at a track painting technique, but the first two were a case of 'keep slapping stuff on until it looks right' sort of affairs! That they did turn our OK was more luck than good management. Today I'm trying out some of the things I thought worked along with one new medium - Vallejo's Model Air 'Rust' paint.

Stage 1 - Flat black base coat

I began by giving these PSC one-piece tracks a spray of Humbrol Matt Black spray and then give it a light coat of Humbrol Satin Varnish on top to protect the base layer from the subsequent experiments (the idea is that I could clean off any further effects/washes without spoiling the basic coat).

I then painted in the 'Russian Green' details behind the road wheels and inside the wheels, which I then masked off for the next stage. (Obviously you will do this slightly differently if you are making a muti-part set of tracks.)

Stage 2 - Vallejo Model Air Rust
Now this is a new medium that I haven't used before. Normally at this stage I would be using a 'rusty' coloured wash or maybe one of AK Interactives enamel washes - I had no idea how this Vallejo paint would look...

Finding it hard to capture the precise colour of Vallejo's 'Rust' with my camera.
It's a metallic and muddy bronze or tarnished copper, if that makes sense?
Hmmm, interesting...It turns out that the Vallejo paint is a metallic dull browny copper colour. Not sure how this is going to turn out at all!

The Vallejo paint is one of it's 'Model Air' paints which are especially designed to be used with an airbrush. I have no idea how light or thick to go with this so I erred on the lighter side (but it dried quite shiny so I don't think you need much).

Stage 3 - Dark wash
In order to pick out some of the raised detail of the PSC tracks I now paint on a thin dark (I use black but it could be a very dark brown) wash. I'm using Vallejo's (no, I don't work for them) Game Color Wash - 73201 Black Shade. This will dull down the shininess of the metallic 'Rust' colour and settle along the extruded track detail.

Stage 4 - Adding the mud/earth
I am returning to familiar ground for this stage as I get out my Humbrol and Vallejo pigments. I look for the pigment colour which is closest to the colour of the mud on the base I am making (remember those pigment swatches I made up recently, this is when they come in handy) which turns out to be Humbrol's 'Dark Earth'...

I apply this in powder form, dusting it over the track generously - over a tray so I can return the excess powder back into the bottle - and then keep brushing until I have a light film of pigment powder over the surface.

You can gently rub away the pigment powder to expose shiny coat underneath.
I will seal this powder layer with a light coat of spray varnish.
Again this dulls down previous colours, which seems over-kill BUT I do think it builds up a rich and deep multi-tonal colour effect (as opposed to just painting the track a flat khaki colour in the first place).

Stage 5 - Highlighting with graphite
This is my favourite fool-proof technique for adding a bare metal accent to any plastic kit. I use a cheap set of Farrel/Gold graphite sketching sticks (but you could use an ordinary graphite pencil) and run the point of a 4B across the raised track detail to produce a steel effect.

Note: The road wheels are still masked out...It case you were wondering.
This brings all the previous stages together and all of a sudden you have a dusty set of tank tracks with a worn pattern on them.

Errata: Spraying varnish over the powder pigment was a mistake! The wet varnish reacted with the pigment and turned the powder a darker shade of the earth colour. Basically the tracks looked like they were black(-ish) again!

So I had a second go - this time (going on a tip someone mentioned in one of my comments) I brushed some Johnstone's Klear (acrylic varnish) onto the track and the dusted on the power pigment. Once dry I brushed off the excess with a stiff brush. The powder stuck this time and retained a more reddy-brown colour.

Revised technique: Dust on a heavy layer of powder on top of Johnstone's Klear
varnish whist the varnish is still wet...
The using a stiff brush clean excess power off.
...Finally re-apply the graphite again.

Conclusion - Was this effective?
This is a different and slightly understated look compared to my previous efforts at weathering tracks.

A prior attempt at weathering tracks where I mainly used pigments on a flat
base coat. A nice effect IF you want heavily muddied tracks but otherwise a
bit over-done really (and not much variation in tonal range).
Before I was - as beginners tend to be I think - a little heavy handed in my application of 'mud' on tracks. You tend to get a bit carried away with the excitement of producing a new effect and so exaggerate it - so my previous tracks tended to be heavily caked in mud. All very well if that's what you want, but not every tank track looks like it's just gone through a muddy watering hole after a heard of buffalo!

In this case I was after a set of dusty and worn tracks where the majority of mud had been shaken off due to the tank driving on proper roads or hardened dirt lanes.

One thing I want to mention is that - as usual with me - I make this simple technique look harder (or more time consuming) than it actually is. This is actually a fairly quick method of doing tracks which has taken me no more than an evening (fast for me) to complete. I say this because I am aware that I see-saw between war-game modelling and display modelling techniques - this is one effect that I think would satisfy either camp.

You will have to judge whether you think the end product is effective. I, myself, like it.