This is a collection of home shop chemistry wisdom I've collected from personal sources and the internet over the years.
REMOVING BROKEN STEEL TAPS FROM ALUMINUM
To remove steel taps from aluminum , use nitric acid
HOW TO DISTINGUISH POT METAL (ZINC) FROM ALUMINUM
Zinc or aluminum? : After 4 hours in NaOH, zinc was untouched. Aluminum was etched in 30 minutes.
A drop of copper suffate solution will turn black on potmetal but won't change color on aluminum. Some pharmacies will have coppersulfate, and it can be found at garden stores.
HOW TO DISTINGUISH MAGNESIUM FROM ALUMINUM
Apply a drop of 1 percent silver nitrate solution to the freshly filed surface of the metal. If the metal is magnesium, a black stain will appear immediately. Aluminum and its alloys will remain unchanged.
ANOTHER USE FOR COPPER SULFATE
When grinding cutting tools to an accurate profile it is difficult to prevent the layout from getting destroyed by the heat of grinding. Neither Dykem blue or magic marker stand up very well. Mix a dilute solution of Copper Sulfate (Blue Stone) and water. A couple of small lumps dissolved into water is fine.
Add a drop or two of Sulfuric Acid (Battery Acid). The acid is not necessary, it just makes it work better. Degrease the toolbit, then paint a drop or two of the solution on the bit. It will immediately leave a thin coating of copper plate on the bit. Wash off in water, then scribe the profile in the copper plate. The copper will not burn off during heating, and since it is very thin, it is possible to engrave extremely fine lines.
ELECTROLYTIC RUST REMOVAL
A plastic tub, a stainless steel or iron electrode, water and washing soda (NOT baking soda!!) and a battery charger. About a tablespoon of soda to a gallon of water.
[ Washing soda is sodium carbonate. Baking soda is sodium bicarbonate. The two are *not* interchangeable. Look for washing soda in the detergent aisle in the supermarket. Washing soda is very basic with a pH of around 11. I'd be very careful to keep it (or lye) from coming in contact with any aluminum parts, which are attacked by strong bases. - MWK]
The iron electrode works best if it surrounds the object to be cleaned, since the cleaning is "line of sight" to a certain extent. The iron electrode will be eaten away with time. Stainless steel has the advantage (some alloys, but not all) that it is not eaten away. The electrode is connected to the positive (red) terminal and the object being cleaned, to the negative. Submerge the object, making sure you have good contact, which can be difficult with heavily rusted objects.
Turn on the power. If your charger has a meter, be sure some current is flowing. Again, good electrical contact may be hard to make-it is essential. Fine bubbles will rise from the object. Go away and come back in a few hours. Rub the object under running water with a plastic pot scrubber. Depending on the amount of original rust, you may have to re-treat. The clean object will acquire surface rust very quickly, so wipe it dry and dry further in a warm oven or with a hair dryer.
The polarity is important!! The surface rust is being converted to metallic iron, so the process is totally self limiting. I have left things (by mistake) for several days: the water was largly gone, by electrolysis, but the object was fine. Reverse the polarity and your object is being eaten away!!! The rust will go along with it, but that's not what you had in mind, is it??
There are lots of variants: suspending an electrode inside to clean a cavity in an object; using a sponge soaked in the electrolyte with a backing electrode to clean spots on large objects or things that shouldn't be submerged (like with lots of wood).
The surface is left black. Rusted pits are still pits. Shiny unrusted metal is untouched. The method will cope with any degree of rust, from surface to heavily scaled.
Use junk iron for electrodes. For electrodes, you can buy cheap stainless spoons at the flea market. The bath will last until it gets so disgusting that you decide it is time for a fresh one. There is nothing especially nasty about it - it's mildly basic-so disposal is not a concern.
One caution: painted surfaces *may* be damaged.
And always remember...
Do what you oughter and add acid to water.
