I found a source for lime putty, so that question is answered. In looking for it I found this info on silicate-based paint. Has anyone tried this? Here is a clip from the site, linked below:

"Silicate Paint Systems
As with limewashes, silicate paints soak into the underlying material, but in addition the potassium silicate binder chemically reacts with the mineral underlying material to form a microcrystalline silicate bond which is insoluble. Secondary chemical crystallisations also take place between the binder, the colour pigment and carbon dioxide in the atmosphere.

The resultant microcrystalline structure has a pore size that allows the free passage of vapour (silicate paints have a very low diffusion resistance equivalent to approximately two centimetres air layer thickness), but the pores or 'holes' are small enough to prevent the ingress of driven rain. The inherent nature of a silicate paint is that of a semi permeable membrane.

Combined with this basic structure, silicate paints employ inorganic fillers and earth oxide colour pigments that are unaffected by the action of UV degradation. The microcrystalline structure is comparable to that of the mineral structure to which it is applied and it has a comparable coefficient of thermal expansion. The insoluble silicates formed in the chemical reaction are resistant to strong acid and alkali attack in the same way that silica sand is a highly resistant product.

As a highly porous protective coating, silicate paints offer a valuable alternative to a limewash, and can provide for much longer life expectancies. There are documented examples of such paint systems performing satisfactorily on lime based render facades in Germany, Switzerland and Norway for periods in excess of 100 years."

Here is a link that might be useful: silicate paint

Very interesting. I couldn't locate what colors you could get using this technique,though. Did I miss it?

They may be hard to find in the US. I did see several under the brand name silacote...linked below. They sell them via EBAY for $1 per sample color.

Here is a link that might be useful: silicate paint distributor.