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Oil stain tidemark in weathering powder on loco

Hi all, following kind advice from Mick Bonwick about oil showing through powder weathering, I had a look at this.  I thought my findings might be useful if you have the same problem, or you are going to start weathering a loco with powders.  These are not meant to be definitive instructions or a recipe success, just my thoughts about what I did and what I discovered, and what I'd do next time. If you cock it up yourself, using any of this material or anything else, then (in the nicest possible way) don't blame me.  

 

How the problem manifested itself... 
I applied powders to the loco, sealing with coats of Humbrol matt acrylic varnish as I went.  As per what I'd read about online if using the powders method.  

I thought it looked ok, but then overnight (not sure how long the problem took) I ended up with a tidemark.  This spread through the weathering, as per pics shown by the red lines.  

 

 

 

 

 

 

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Investigating the problem...
RMWeb (Mick Bonwick) provided insight into the 'Bachmann Tidemark' which is when oil inside the body (and in joins within the construction of the body) is moved through the gap and into the matt powder weathering through capillary action, to form a tidemark.  

 

 

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A failure to find Isopropyl Alcohol...
Mick Bonwick's suggestion was to deal with the Bachmann Tidemark and suggested Isopropyl Alcolhol, IPA, rubbing alcohol.  It seems this chemical was tricky to find anyway but had become popular as  cheap DIY sanitizer during the coronavirus lockdown.  The chemists I tried didn't stock it, and I didn't fancy chancing my arm with dodgy chemicals (which may or not have been the real thing) on online market places.  

 

 

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My approach...

Step 1...
I therefore washed the entire loco body (after removing it from the chassis) in a mild solution of tepid water and fairy liquid.  Transfers weren't a problem for me - there was no damage to these.  They weren't the original Oxford Rail transfers, they were from Fox Transfers.  I used an old toothbrush to scrub away at the body to remove the weathering and especially around the areas affected, and to scrub the inside of the body.  2 wheel arches (splashers) came away but were undamaged and easy to glue back on.  The brass name plates came off too.  I then let it all dry and glued the items back on.  

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My approach...
Step 2...
Once dry, I gave a good thick coating of Humbrol enamel gloss varnish to the inside of the body to seal it and any gaps, so if oil remained or built up due to being sprayed around by the motor, it hopefully wouldn't be able to penetrate through to the matt weathering and have the same capillary action effect to create a tide mark.
Once dry, it was noticeable that a tiny bit of the gloss varnish had itself seeped through, in a few places.  This was fixed with a quick light brush of Humbrol matt paint of a close colour over the gloss enamel varnish - there was no perceptible problem with the paint finish which I gather may occur when applying acrylic over enamel.  Maybe that was due to the tiny area in question. Pics show inside although the gloss varnish doesn't show up.  

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My approach...
Step 3...
I the reapplied weathering powder and varnish spray as before, not to any great degree as I didn't want to waste time if the same thing happened.  Upon drying, there was still an oil tidemark in 2 places, notably between the windows of the cab, where it had been worst before. But it definitely wasn't as bad there, and it didn't reappear in the other places again  I therefore concluded that washing in detersives, and a layer of varnish inside, was definitely useful. 

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My approach...
Step 4...
I also concluded that if the powder wicks the oil out of the cracks, maybe I could use that to my advantage like spillsorb or fullers earth for the remediation of liquid chemical contamination. I therefore applied a small pile of loose weathering powder (specifically Humbrol smoke weathering powder) and left it for a few hours.  I then took it outside and blew off the excess, and helped the last bit with a cotton bud.  The cotton bud left a tiny bit of scuffing to the weathering powder but not too bad, showing the slightly bumpy mark in the photo in front of the round cab windows.  Importantly, the powder had wicked away the oil.  The other place there was a oil tidemark remaining after round 2 was on the tender around one of the equipment lockers (or whatever it is) on the top I therefore applied a loose pile of weathering powder, left it an hour, blew it away, and the oil tidemark was gone completely.  
I then did more weathering using powder and spray varnish, and was relieved to see there was no more oil tidemark. 

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My approach...
Step 5...
After another coating of weathering powder and spray varnish....

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Of note, the weathering powder really highlighted the moulding seam along the length of the boiler.  I therefore applied a fine emery wet and dry paper over the seam.  Obviously this left patches along the boiler, but a couple of coats of powder and varnish and these were no visible, the powder covered it up.  

Photos show a before (angled shot, you need to zoom in!) and after shot (side-on shot).... 

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I then reattached the bodies to the engine and tender, applied more powder until I got the effect I was after (being careful to avoid getting it into the wheels and mechanism), cleaned the wheels with Humbrol enamel thinners, and bob's your uncle... one weathered loco with no moulding seam line, no oily tidemark and running nicely.  

I did try to clean the powder/varnish of the small windows, using a cotton bud and enamel thinners, but the cotton bud was too big and it started to mark/remove the weathering around the glass in a rather obvious way.  I therefore decided I could live with grimy windows but I couldn't live with messy shabby marks around them, so touched up the powder and varnish, and hope the tiny model crew get their act together and clean them at some point in the future.  

I touched up the handles to the reversing lever and 2 brakes on the tender (or whatever they are) with Railmatch oily steel.  I painted the buffers to include a a bit of a more worn metal centre patch.  It was then ready for crew, fire irons and coal.  

Some photos of what I think is finished... I'm trying to depict a GWR wartime black Dean Goods in late war level of dirtiness, I've based the grey/dust colouring and level of obscuration of the markings on photos of black locos in the 1950s.  

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So for my next loco to weather, I reckon I'll give this sequence a go...

 

1. Remove body from chassis.

2. Do any weathering to wheels/chassis as desired (being careful with powder in the motion)

3. Wash the body twice in mild fairy liquid tepid water, allowing to dry after each wash.

4. Apply Humbrol gloss enamel varnish liberally inside... two coats allowing to dry between each. 

5.If gloss varnish seeps through, touch up with chosen colour to match base colour of matt acrylic Humbrol paint. 

6. Apply a loose pile of weathering powder over the body to wick away any oil.  Then blow away to remove, maybe finish removal using a cotton bud or something.

7. Do a simple coat of weathering powder and varnish... check for any wicking / tidemark and if necessary apply another coat of loose powder. Worst case would be to wash again and re-varnish the inside, and repeat with loose powder, until no oil stain appears. 

8. Progress to doing the actual weathering using powder and spray varnish.  

 

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I have had the same problem with Bachmann locos although I only weather with enamels.

The first step for me is to dismantle the chassis and get rid of the excess lubricant, Bachmann appear to put 4 times as much lubricating grease as is required. You need to stop the lubrication from being thrown up from the chassis.

i have found that I need to make 2 passes with the Isopropynal and then wash with mild detergent. The lubricant is really difficult to get rid of.

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That's a good result! Most impressed with your determination and resolve. You could prevent some of your intended work, though, if you gave the mechanism a jolly good clean first. In the absence of isopropyl alcohol you could use paper towels and cotton buds to remove the excess grease. The grease gets spread around the inside of the body as soon as the mechanism turns the wheels. Clean everything before running it in.

 

For cleaning spectacle plates I find these useful:

 

https://www.scalemodelshop.co.uk/product/50x-small-triangular-cotton-swabs-tamiya-87106

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