Rust removal

Method

Make a solution as follows:

1. 1 Litre of water
2. 100g citric acid
3. Choose one from:
   1. 40g sodium carbonate (washing soda), or
   2. 63g sodium bicarbonate (baking soda), or
   3. 30g sodium hydroxide (caustic soda

The stoichiometry and performance are equivalent for any of the three alkali ingredients.

Immerse ferrous parts in the solution until the oxide is reduced. Does not remove iron from the part (unlike vinegar), so parts can be immersed for extended periods without damage.

Optional gel

5 tbsp corn starch

75ml water

10 drops washing up liquid

Add corn starch to the cold water, then bring the main solution to a boil and stir in the corn starch. Stir continuously until thickened then allow to cool. Add the washing up liquid. Gel is extremely convenient to paint on large parts. Cover the coated parts with clingfilm to avoid drying. Let sit for 15 minutes plus, then rinse off.

Tips

Optimum performance is at 50C, but performance is good at all temperatures. The usual contact time is 15 minutes for light to moderate rust, up to 24 hours or more for extreme corrosion.

Using in an ultrasonic cleaner will help with rusty and unclean parts.

This may not be entirely safe in parts containing aluminium but the pH is about 5 so any corrosion of non-ferrous metals should be only slight, especially given the brief contact time.