I get a lot of questions regarding Tumbling and Polishing Metals. So here goes!

You have a few options: By Hand using a dremel, nail file buffer, pro polish pad or auto sol or using a tumbler.
The quickest and easiest option is tumbling.

Tumbling and Polishing Metal

Metal tumbling is used to burnish, deburr, clean, radius, de-flash, descale, remove rust, polish, brighten, surface harden, prepare parts for further finishing. This is done using a rotary rock Tumbler. With either a Rubber or Plastic Barrel. The metal is placed into the barrel with the correct weight of stainless steel Ball bearings and liquid soap b. You can also use the green coloured Fairy washing up liquid. The correct weight of ball bearings will be determined by the size of your tumbler and the amount of blanks you are polishing.

For each process you must use a different barrel. If you chose to deburr your blanks with ceramic medium, its best practise to have a separate barrel for deburring and a separate one for polishing. This is because any fine particles or residue that have been left behind from the ceramic media can damage the blanks when polishing them. We will be talking about polishing metal such as Aluminium, Copper, Brass, Sterling Silver.

All of our New Blanks will be de-burred and have the laser nobble removed, we have the option for them to be tumbled for you. So lets focus on getting them nice and shiny.

We use Rubber Barrels for Tumbling Metals. As they are much quieter than plastic ones and are much kinder to the metals. With Aluminium as it is a soft metal it can dent and scratch easily, this can happen in the tumbler when smaller shot is used and when using a plastic barrel as the small shot will ricochet off the plastic barrel into the blanks which can create a pitted effect.

We use Stainless steel shot, also called Polishing Media or Jewellery Mix.  Stainless steel shot is the best investment for polishing metals. It has anti tarnish properties and can be kept in water while not in use, so that you do not have to dry it off like steel or chrome plated and it doesn't smell terrible like Steel or plated shot does when wet.
When you get your shot, wash it first to clean off any dirt that could be on there. Put the shot into the tumbler with some Liquid soap, either washing up liquid or soap b and run for an hour. 

Polishing Instructions

For Aluminium we recommend shot no smaller than 3mm, in a 3lb barrel we suggest between 250g and 400g.
Place the shot in the bottom of the Barrel, add water to just cover the shot and add the blanks in.
I have seen it advised where people say to cover the blanks and shot in cold water. However I have found that this can leave aluminium with a residue and duller than required.
The way the liquid soap works is that as the barrel rotates the soap activates and expands as it bubbles, it attracts the grease and dirt away from the blanks as the shot is moved against them to loosen the dirt and harden the metal. The bubbles suspend the dirt, until you finish the cycle and drain the contents out into a sieve and wash with cold water.
Too much water will allow the dirt to be re applied back onto the blanks and not enough water will not allow the dirt to be removed to start with.
Too little soap will result in dirt not being suspended and the blanks rattling around in the barrel which can damage them and dull them, and too much Soap will be a nightmare when you open it as it will foam out everywhere.
1 drop or tea spoon of soap is required.
Seal the lid of the tumbler and place onto the base and switch on.

How long you leave it on for is up to you to decide and it is trial and error. It depends on how shiny you want your blanks to be. The longer you leave the tumbling process the harder your aluminium will be, as tumbling works to harden the metal. 

Tumbling Time Guide

1.2mm = 1hr
1.5mm = 1.5hr
2mm= 2/3 hr

Tumblers

http://www.littlefreckle.co.uk/jewellery-polishing...