Nautical Research Journal Tips & Techniques


Cleaning brass parts for blackening, plating or painting By Kurt Van Dahm


If you use brass in building your models the parts are usually blackened, plated or painted to replicate the appearance of the full-sized part.


Instructions for the use of blackening agents, plating solutions and paints always call for a thorough cleaning of the parts. First remove the excess soldering scale from the parts and clean off any oils or grease. Next it is advised to pickle or etch the parts prior to blackening, plating or painting.


A good way to accomplish both a thorough cleaning and pickling at the same time is to use Sparex No. 2 (Sparex). Sparex comes as a dry 98-percent concentration of sodium hydrogensulphate, also known as sulfuric acid or sodium bisulfate, that is dissolved in water to make a usable solution. Most commonly sold in plastic bags (Figure 1), a ratio of 1/8-cup (2 tablespoons) is mixed into 1 cup of water to make one quart or one gallon of liquid. It is advisable to protect your hands and eyes when mixing and using Sparex and keep it off any clothing you want to keep hole free.


Sparex works best if heated but not boiled. I use a small crock pot for this as it will heat the liquid but not get hot enough to boil it. Jewelers’ supply stores sell small crock pots, but I have found them at secondhand shops like Goodwill for less than $5. Try to get one with a cover so the solution does not evaporate between uses. Other means of heating Sparex can be to use an immersible coffee heater meant to heat a single cup of coffee. Whatever is


375


1. Sparex package


used to heat the solution, it is vital that the Sparex does not boil. If there will be long periods between uses it is best to store it in a resealable plastic or glass container with a plastic lid—and keep it away from ferrous metals.


Use copper tongs for removing parts from the liquid. Metal tongs will contaminate the Sparex and make it into a copper plating bath. Everything will come out covered with a thin layer of copper.


Mix the Sparex and luke warm water according to the directions provided on the Sparex container and bring the solution up to heat in the crock pot or similar container. Put the parts to be cleaned into the Sparex


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