Well, firstly, I started off by giving all of the parts that were going to be treated a good going over with Carr's Acidip to chemically clean the surfaces thoroughly, and to get rid of any traces of flux, dirt and so on. After this, it was into some plain water in my wife's jewellery cleaning ultrasonic tank...
This always does a superb job at making any remaining grime and noxious substances literally fall off the model. You can even see the slightly cloudy water streaming away from the model when you switch the machine on. And she is happy as well if you offer to clean her rings at the same time - although preferably without the application of Acidip!
After this, the parts were popped on some kitchen paper in a box to keep the dust off them and left to dry thoroughly in the sun. Such are the joys of modelling in the summer.
After this, I reached for the Casey's Gunblue, and applied it with the end of a cotton bud. Unfortunately this was the result - distinctly patchy.
I'm not quite sure why. The model wasn't handled at all after cleaning, and was perfectly dry. I can only hypothesize that it was variations in the grades of nickel silver that made the difference.
Either way, I followed it up with a thin coating of etch primer, sprayed on, to ensure that the paint would adhere properly. I'd washed the remains of the gunblue off with plain water so the surface for the primer was clean again.
So quite a disappointing result. I still see the merits of using blackening on the edges of models to ensure that any paint chips won't be so obvious. That makes a lot of sense, and I'll be doing it in limited circumstances. I also suspect that the gunblue will "take" better on brass than on nickel silver, so I haven't given up all hope of this method.
I thought that I'd post the results so that you can all see what the outcome was, and perhaps add your own thoughts or experiences.
Acidip is a good flux neutraliser, but the surface of the metal was still contaminated, and possibly oxidised.
ReplyDeleteBefore blackening etched brass, clean the metal with Carr’s Surface Conditioner. This removes any oxidation and etches the surface of the metal in preparation for the blackening solution, and in so doing causes the metal to turn a matt yellow colour. Rinse in hot water and dry.
Either immerse the metal in the blackening solution and rub with a cotton bud, or apply with the cotton bud, but whichever method used, keep rubbing, and don't leave it too long before rinsing.
I often dip in the solution and rinse two or three times until happy with level of blacking .
If the solution is too strong then the blackening may begin flake off - let the solution down with a little water and try again.
Thank you for that. I have never used the surface conditioner before, as I had never seen the need for it. All is now clear...
ReplyDeleteI've used the Carrs metal blacking many times successfully, but only on much smaller items such as couplings and handrails, where they are small enough for the patchiness to not be obvious, and they can be physically cleaner with a glassfibre brush.
I'll be at ExpoEM next Saturday, so I'll make sure that I pick up a bottle of Conditioner.