Pink cases

[John MH]

It’s unlikely to have weakened the cases to any measurable extent but if there is any doubt use caution.

[Meaty]

Thanks for all the replies.
2 caps was way under the suggested dose on the bottle and I thought that it would be a safe starting point-christ, had I used the 'correct' dose I think they would have probably melted! I can see this stuff lasting a very long time as I brought 4 bottles (it was on offer in Maplins)
I think I will try a few loads on 50-60 grains first and work back up to my usual 75-80 grain load.

[channel12]

I'm assuming they are blackpowder cases, my procedure is to drop them into hot soapy water and use a nylon bristle brush on the inside. When they are dry put them in the tumbler for a few hours for a final polish. I don't use acidic cleaners because they dissolve the brass.

[The Cupcake Kid]

The pink tarnish you may sometimes see on brass is just what John & Magpie has said - Zinc/Copper leaching from the brass leaving a residue of copper. I see it every now and then, usually if the brass has been left in the cleaning solution for a while.

It could be nothing to do with the cleaning agent you're using but might be something in the water you're using (presumably tap water?). Using distilled water to make up your cleaning solutions may stop it happening, but that's too expensive for most people.

I wouldn't worry about it weakening the brass as it's happening on a microscopic level on the surface of the metal and a miniscule proportion of the metal will be affected.

As for acidic cleaners, they are fine as long as you follow the manufacturers guidelines and make them up in the concentrations recommended. I have used Citranox on my brass for years in a very dilute solution. It goes a very long way and does an excellent job whether used in an ultrasonic bath or SS media tumbler.

[Meaty]

Thanks for that,
I drop my cases into an old milk carton with a solution of tap water/screenwash as soon as they are fired as it helps to keep the fouling soft (or so they say) but with this batch they were sitting in the solution for a few days before I got round to cleaning them in the ultrasonic, so what you say makes a lot of sense now. For the cleaning tank I use boiled water out of the kettle that has been left to cool for a while.

[ColinR]

I use citric acid (CA) in my ultrasonic cleaner and sometime get a pink tinge, but not always. I use 2 table spoons of CA in 2 litres of water and heat the tank to 75 degrees and dump in the brass without any prior treatment other than removing the primers. It works a treat. I have long suspected the copper leaching is due to something in the water or a particular impurity as I use food grade CA and it does not always happen. Brass comes out bright clean inside and out and especially the primer pockets. I wonder sometimes if it is a timing thing - I usually leave them in for about 30 mins but sometimes maybe longer.

[bigfathairybiker]

The pink colour is the colour of new copper.
The browny colour of copper normally seen is the colour produced by copper oxide ( Cu2O )
There is another copper oxide ( CuO ) which is black.

The pink colour on the brass is due to the cleaning action removing the oxides from the copper and allowing the original copper colour to show. The effect is only microns deep and does not affect the case integrity.

The reason that the colour of the copper can actually be seen is due to the fact that brass is a mixture ( alloy ) of copper and zinc, but not a full chemical compound. So therefore the properties of each metal can still be found. You can get other colours like the silvery colour of zinc by using other chemicals and a little heat.


Cheap cola ( contains citric acid ) cleans brass very well.
But ammonia based cleaners can cause what is called "stress corrosion" which leads to the brass weakening and cracking. Cases cleaned with ammonia need to be annealed to avoid the problem.

Polishing the cases removes the cleaned copper and also oxidises it due to the heat produced by polishing and the oxygen in the air.

Just thought I'd clear this up.

Mark

[bigfathairybiker]

I've been talking to a friend about this further and we have come up with a more likely cause than the one I described above.

The action of the chemicals "etches" microscopic imperfections into the surface of the metal.
These imperfections reflect pink light more than other light causing the pinkish colour.
Polishing the metal removes/smooths out the imperfections removing the pinkish colour.

This effect also happens in other metals and the "colour disappears when polished" bit gave it away.


Mark

[The Cupcake Kid]

dezincification