How to Choose the Right Solvent for Making RSO
Ethanol vs Other Solvents
Not all alcohols are created equal! And not all solvents are food safe like pure ethyl alcohol (ethanol). Be cautious, aware, and specific when choosing the alcohol you use to make RSO. Always avoid toxic solvents like isopropyl "rubbing alcohol", mineral spirits, denatured alcohol blends, or any hydrocarbon derived solvent like butane, propane, pentane.
TLDR: Only ethyl alcohol (ethanol) is safe for making RSO or FECO!
Ethyl Alcohol - Ethyl alcohol is the best, safest, most effective option for alcohol when making RSO. Sometime available at local retails in concentrations as high as 95% ABV (190 proof), however many states including California, Florida, Ohio, Pennsylvania, North Carolina, and Maine currently restrict the strength available at local liquor stores to 151 Proof (75.5% ABV). Thankfully, reputable online retailers of pure 200 proof food grade alcohol have emerged to fill this need for a high-proof food safe solvent while, while also abiding by the individual state rules and regulations for alcohol. If you live in one of the states listed above, you are able to purchase 200 proof pure food grade alcohol without worry of additional permits, regulations, or license fees.
What to do: Source only pure 200 proof food grade ethanol when making tinctures, or concentrates including RSO/FECO.
Naphtha - The original solvent used by Rick Simpson in the early 90's when he was developing his recipe and process for making a concentrated oil from cannabis, with his intention of topical application only to his skin. This choice to use naphtha was made when other, better, solvents like pure food grade ethanol were not available for purchase, so he went to the drawing board and returned with naphtha as his recommendation. RSO made with naphtha can still contain small (0.5%-2%) concentration of the solvent dissolved into the oil, which can create additional health concerns due to the toxicity of naphtha if the RSO is consumed orally vs topically.
What to do: Avoid naphtha as an ingredient when making RSO.
Isopropyl "Rubbing" Alcohol - While generally more available for purchase at high ABV concentrations ranging from 70% - 90%, isopropyl alcohol will dissolve cannabinoids similarly to ethanol. However, as mentioned before that not alcohols are created equal, isopropyl alcohol is toxic if consumed and should not be used to make RSO.
What to do: Avoid isopropyl alcohol as an ingredient when making RSO.
Denatured Alcohol
200 Proof vs 190 Proof for RSO
Solvents chosen for RSO recipes should not contain as little water as possible. The more water in solution (Everclear 151 contains 25% water!), the longer the evaporation stage to reach concentrated oil will take. This added time required to evaporate will typically result in a very dark final oil that has been over decarboxylated which can have significant effects on the final "feel" of the RSO. Look for solvents that state "0% water" or are listed as "200 Proof".
More information about 190 proof vs 200 proof for alcohol tinctures.