As ever, it looks crap in the Blogger interface. Double click in the image to see the chart in full 650 by 500 pixel glory.
How to prepare the chart.
First the data. I downloaded the longest available time series of prices, back to 1987, from Indexmundi.com. I saved this as a comma-seperated values file in my 'R' working directory. I added to this .csv file the latest September aluminium price, US$1962 per metric tonne, from the London Metals Exchange website.
Here is the script. It may also be used with 'R' under Windows.