Chemically blackening brass and steel.

[ROSSPOP]

I have just completed a loco kit build in 7mm and there have been chassis parts that are likely to gum up if contaminated with black paint and I have been unwilling to leave them plain brass.

Problems areas have been the brass bearings and brass hornguides as well as a sprung compensated bogie.

 

 

 

At the same time I thought I would like to try my hand at blackening steel wheel rims and their axles and use this method as a means of avoiding the laborious task of painting wheels.

Having researched other modellers experiences and advice on modelling forums I have chosen to use Birchwood Casey blackening products.

Blackening steel does not reduce rusting and so I have chosen Carrs Electrofix as an application to inhibit rust and also the rusting up of the wheel securing screws.

 

 

 

I also used a quality  black etch spray primer for the first time.

 

Some modellers using this technique apply the blackening chemicals slowly using cotton wool buds but others have tried mixing these chemicals with water and dipping parts in a solution to cause a blackening reaction.

 

I chose the dipping process.

 

All parts to be blackened need to be very clean and , again, following the experiences of others I chose the following cleaning procedure for speed and efficiency.

 

1.   clean with Viakal.

 

2. rinse with clean water.

 

3. clean again with methylated spirit.

 

4. dry using a hair dryer

 

5 Avoid handling parts  prior to  blackening.

 

 

 

I  blackened the bogie frame first and then reassembled everything after blackening the bearings, screws and hornguide plates seperately.

 

THESE PRODUCTS  ARE POISONOUS AND A  SKIN IRRITANT SO WEAR GLOVES AND TAKE CARE.

 

I used Brass Black for all brass parts and Super Blue for steel parts.     Interestingly, Brass Black will also blacken steel (but not so well in my view)  Super Blue can be  quite ineffective at blackening brass.

 

With mixing with water as a solution it really does`nt matter about the ratio of blackening agent to water, but the weaker the mix the longer it takes to blacken.

 

What does matter is how long you immerse the parts.  Using the above mix a first immersion for 20 seconds was enough any further is likely to reverse the process and the blackening effect rinses off !!!   Immediately after each immersion a plunge in water will stop the reaction.   This is followed by drying with a hair dryer and `buffing up` with a dry paper towel to remove the black dusty residue.  If further blackening is needed after drying and buffing then a further immersion for 10 seconds has been enough without any detrimental effects.

Again, rinsing in water after every immersion.

 

For the  steel wheel tyres and axles  etc, I used the same mix ratio of 50-50 and cleaned prior to immersion as above. And, again , no longer than 20 seconds for the first immersion.

 

I then used  clean paper towel dipped in Electrofix   to `seal` wheel tyres and axles 

 

 

 

I followed the same process for the rest of the chassis hornguides and bearings etc.

 

 

 

as an experiment I also blackened the coupling rods and crankpin bearings  ( washers would`nt blacken )

 

The rest of the chassis was sprayed with Clostermans etch primer.

 

So far I have been pleased with this first time use of blackening chemicals.......

 

But I`ll let you decide........

 

 

 

 

 

 

[bertiedog]

Very neatly done, at work we used copper carbonate blackening for brass, and selenium gunblack for steel.

 

There are lead removing acids available from Carrs to eliminate most of the soldered areas, or you can grit blast, or soda blast, which is gentler on fine brass. The grit blasted surfaces on brass are truly black with the carbonate process, used in fine optics internals to prevent reflections. Bicarbonate of Soda is a good clean up blast material, cheap and harmless, leaves brass with a smooth sheen. A soda blaster can be made at home easily, mimicking the action of an airbrush with soda powder rather than paint. this assumes you have a small compressor of course.

 

Copper Carbonate is dissolved in Ammonia till saturation, and the cleaned brass is immersed till black, usually a few seconds, at a temperature of about 80 degrees centigrade. A sacrificial piece of brass is used to test and "prime the hot mixture". The pot of the mix lasts ages, just top up with more carbonate.

 

Carbonate blackening also works on bronze, but does not give black, but brown, as the process was invented by the Victorians to age new Bronze castings

 

There is another option and that is black nickel plating, kits are on the market to do the process, but only worth it for quantity work.

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Carbonate and other blackenings on brass does vary with grade of the brass, some sheet brass just will not take the finish if they are hard brass.

 

Stephen.

[ROSSPOP]

Thanks Stephen for the extra knowledge........ I was wondering about the soldered areas.... I shall ponder on that for the next effort.

 

This is like a hobby in itself.......

 

 

John