Dipping method to blacken DG couplings (or any small part)

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Dipping method to blacken DG couplings (or any small part)

Postby Phil Copleston » Tue Feb 07, 2012 12:22 am

I was bending up some 2mm scale DG couplings a while back but didn't want to leave the brass bare, nor did I want to paint them which is messy, clogs up their delicate action, and leaves brass showing through should I accidently chip the surface. So chemical blackening seemed the way to go.

I found the Carrs range of blackening chemicals easiest to use, are readily available for purchase, and give consistent, measurable results (usual disclaimer). You can get these direct from C&L Finescale via mail order http://www.finescale.org.uk/index.php?o ... &Itemid=57 or find their products at shows. Other similar products are available elsewhere.

My method for blackening is rather like the old three-stage chemical photo-developing process. I arrange three small glass jam jars in front of me – one for acid dip (to clean the brass), one for plain water (to rinse or halt the process), and one for chemical blackener (to darken the brass). Carrs also sell a "neutralising rinse" but I find that water works just as well. Working methodically and consistently (timing), I find controlled results follow every time.

For those who may be hesitant to have a go, here is what I do in five clear steps:

    1. Follow the DG instructions and make up a goodly supply of couplings (or whatever you intend to chemically darken) in one sitting. Tedious I know, but it gets this part of the process out of the way and you’ll end up with a whole batch ready to fit. I also use the handy DG loop-bending jig (separate purchase) to help get all the loops consistent.

    2. Take a piece of scrap wire about 150mm long, bend a deep hook on one end and use this as a fishing tool. String several couplings by their loops on to the hook ready for dipping.

    3. Having arranged your three jars of acid dip, water rinse and blackening agent in a row in front of you, prepare to dip the couplings. First pop the hooked wire with its catch of couplings into the acid to strip away any grease or dirt, then pop them into the water rinse, then briefly into the blackening agent, and finally back into the water again to stop the chemical action of the blackening. It only takes a few seconds for the blackening process to work!

You might find some explanatory footnotes helpful at this point:

a) The use of acid dip is important to achieve consistent, all-over results.

b) You will find though experiment (use a piece of scrap DG etch) that the blackening process increases over several seconds, from barely discoloured to slightly brownish, then from a darker brown to black, and eventually to a horrible powdery black (over processed!). I find the most effective and most realistic tint to go for is a medium brownish colour (not black) which takes about 30 seconds max in the blackening agent. Tip: It is better to under estimate timing and have to repeat the process to build up the colour than to ruin everything by over doing it in one hit. Make notes and use a photographic timer, a clock or watch's second hand, or a mobile phone’s stopwatch facility for consistency of results. Practice makes perfect.

c) The phosphor-bronze wire coupling loop and steel uncoupling dropper wire will colour slightly less than the brass, but this is not worth worrying about and I think looks better than "solid colour" on the loop anyway.

d) Use a sheet of newspaper to protect your work surface from corrosive drips.

    4. Place the newly "blackened" DG couplings on a kitchen towel to air-dry. Repeat process for the rest of the batch. You should now have a supply of top-quality, high performance, low-visibility delayed action auto-couplings.

    5. Fit to rolling stock and tweak as per DG instructions, install below-track electro-magnet uncouplers, and prepare to have fun shunting your trains hands-free! Once installed correctly and darkened chemically using this method, you will hardly notice them in future (which is the point).

I like to use DGs on my 2mmFS rolling stock, but you can, of course, use the above dipping method for other coupling types – I prefer three-links on my S scale models.

Blackening of many other items prior to painting, such as handrails, lamp irons, etc., I find is also a good idea as it stops chips showing through as bare metal. Use a separate whitemetal blackening agent on cast items, which Carrs also sell. Paint also adheres better to blackened surfaces and is more chip-resistant.

Here’s a further thought: Rather than dipping components, try applying the process directly to an existing model in chip-prone areas such as footplate valances and cab roof edges, using cotton buds separately charged with the different chemicals and water in sequence (as outlined above) to achieve the same effect in very limited areas. I haven’t tried this myself, but it should work just as well.

Hope you find my experiments with dipping methods for blackening brass helpful. Let me know how you get on!

Phil
Last edited by Phil Copleston on Tue Feb 07, 2012 12:41 am, edited 1 time in total.
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Re: Dipping method to blacken DG couplings (or any small par

Postby Richard Oldfield » Tue Feb 07, 2012 12:41 am

Hi Phil,

Thanks for a (for me at least) challenging posting.

Many many years ago I had one or two tries with chemical blackening, certainly overdid it and ended up with an unsatisfactory result. It's high time to re-visit this technique as I'm often touching up bare metal following minor mishaps or simply coupling/uncoupling.

Cheers,

Richard
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Re: Dipping method to blacken DG couplings (or any small par

Postby Phil Copleston » Fri Feb 10, 2012 9:31 pm

Happy to 'challenge' you, Richard - give it a go!

I find that Carrs' products work well for me, but have you or anyone else got experience of other manufacturer's blackening products?

Phil
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Re: Dipping method to blacken DG couplings (or any small par

Postby Wally » Sat Feb 11, 2012 12:54 pm

Phil Copleston wrote:Happy to 'challenge' you, Richard - give it a go!

I find that Carrs' products work well for me, but have you or anyone else got experience of other manufacturer's blackening products?

Phil



This is the result of using Birchwood Casey Brass Black on the chassis of a small Peckett loco whic has been for a (too) long time sitting in my "to finish" pile.

DSCF1798.JPG


There is no obvious chipping after all these years and it does not require the acid dip to preclean the surface, just a good bubling in the ultrasonic bath prior to application.

One other point which is often overlooked with chemical blackening is that it renders small parts impervious to soldering, a useful point when assembling things such as valve gear.

Wally
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Re: Dipping method to blacken DG couplings (or any small par

Postby Phil Copleston » Sat Feb 11, 2012 2:49 pm

Hmmm... good point Wally - about rendering small parts impervious to soldering. Useful tip that. On the other hand, make sure you've got all the parts soldered in a sub-assembly before blackening (like my DG couplings)!

I came across this article and ad after Googling "chemical blackening":
http://www.mmsonline.com/articles/do-it ... blackening (some useful additional advice here)
http://www.black-it.co.uk/index.html

Not used Birchwood Casey Brass Black myself. I know various authors in MRJ recommend it. Where can I buy it - at shows (like Eileen's) or hardware stores?

Phil
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Re: Dipping method to blacken DG couplings (or any small par

Postby Richard Oldfield » Sat Feb 11, 2012 6:33 pm

Hi Phil,

I had a rummage at the club today and turned up a bottle of the Birchwood Casey Brass Black (as per Wally's posting) so I'll be having a go with that next week and will upload some images.

Cheers,

Richard
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Re: Dipping method to blacken DG couplings (or any small par

Postby Cock Sparra » Sat Feb 11, 2012 7:09 pm

Phil Copleston wrote:
Not used Birchwood Casey Brass Black myself. I know various authors in MRJ recommend it. Where can I buy it - at shows (like Eileen's) or hardware stores?

Phil


Hi Phil

Yes Eileen's do do it three sorts use the super blue, the one that say's it's for brass is not so good on brass. I've tried both, not used the ally one.
Cheers Phil

I used to be normal but I'm better now
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Re: Dipping method to blacken DG couplings (or any small par

Postby Phil Copleston » Sat Feb 11, 2012 8:37 pm

Richard Oldfield wrote:I had a rummage at the club today and turned up a bottle of the Birchwood Casey Brass Black (as per Wally's posting) so I'll be having a go with that next week and will upload some images.


Richard,

Excellent news, I look forward to hearing how you got on with the stuff. I think the secret of success is to get the metal surface scrupulously (chemically) clean before blackening, then experiment with the timing to achieve the desired depth of colour. Dang it man - you'll be blackening everything in sight next!

Phil
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Re: Dipping method to blacken DG couplings (or any small par

Postby Phil Copleston » Sat Feb 11, 2012 8:41 pm

Cock Sparra wrote:Yes Eileen's do do it three sorts use the super blue, the one that say's it's for brass is not so good on brass. I've tried both, not used the ally one.


Thanks Cock Sparra, that's handy to know. I'll pick up a jar of the stuff to play with next time I bump into Eileen's at a show (which won't be long!).

Phil
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Re: Dipping method to blacken DG couplings (or any small par

Postby Wally » Sat Feb 11, 2012 8:43 pm

Cock Sparra wrote:
Phil Copleston wrote:
Not used Birchwood Casey Brass Black myself. I know various authors in MRJ recommend it. Where can I buy it - at shows (like Eileen's) or hardware stores?

Phil


Hi Phil

Yes Eileen's do do it three sorts use the super blue, the one that say's it's for brass is not so good on brass. I've tried both, not used the ally one.


I hate to disagree with the chap who is going to buy the beer tomorrow lunchtime, but, you may need to agitate it with a cotton bud during the application process, to assist the reaction, in some cases as stated in the instructions.

Wally
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