Causing a metal or glass marble to float in an aqueous solution I am trying to find a way that you could cause metal (Aluminum) or glass to float in a mixture of water and some water-soluble material. I am aware that salt can be used to heighten the density of water, but I doubt it could go to that extent because both aluminum and glass are more dense than salt (possibly flawed logic, I have limited knowledge of the subject). So basically: if there is any way to cause Aluminum or glass to float in water, possibly through adding a water soluble material to the water, please let me know.

Edit: Basically what I'm doing is trying to think of creative ways to sort materials by density, for example a set of marbles. With the example of solutions with salt, you would vary the amount of salt in the mixture to alter what materials would float.
The best current non-toxic alternative to Clerici Solution appears to be Sodium Polytungstate (SPT).  It also has a neutral (~7) pH, which is important when working with aluminum. By dilution/evaporation, density covers the range $1.1\!\!-\!\!3.1$g/cm$^2$, but above $2.5$g/cm$^2$ it can develop a harmless reversible blue tint when exposed to reduced metals. Aluminum has an oxide patina, so I am not sure if it qualifies as a reduced metal in this setting. SPT is rather expensive though.
Aluminum is $2.7$ g/cm$^2$ and Common glass is $2.52$ g/cm$^2$. So both of those materials, many gemstones and some minerals, will float in SPT.