What is denatured alcohol, and what is the difference between that and rubbing alcohol? I have a houseplant h?

Just use a product designed for scale on a houseplant. Any garden center will have 3 or 4 options for less than $10.

http://www.ehow.com/facts_5652728_isopropanol-vs_-...

I use rubbing or isoprop-alcohol for treating mealybugs on houseplants. I'm not sure the scale will fall to the alcohol since the shell is designed for protection. Normally with scale you need a systemic poison. Still, give it a try, pick the scale shell off first, that will help.

* Methylated spirit (Meths or denatured alcohol—yet not rubbing alcohol, that's distinctive is ethanol which has been rendered poisonous or in any different case undrinkable, and each so often dyed. * Rubbing alcohol, united statesP. / B.P. is a liquid arranged for topical application arranged from specifically denatured alcohol and containing sixty 8.5-seventy one.5% vol./vol.