best thing i have read to use is a grain alcohol like everclear (190 or 195 proof) take 7.5g of good bud and break it up/grind whatever.. place it into an air tight container. Pour 2 oz of everclear over it letting it sit for at least 48 hours.. get a cheesecloth or strong coffee filter and strain the mixture ringing out the stuff as good as you can.. you can either use it now or try to slow cook it down some which risks fire.. apparently .7 ml is a small dose, 1.4ml is a very nice heavy stone. .7 ml i think is about 15-20 drops so ya need a lot more than a few drops under the tongue.. maybe if you can boil it down enough to evaporate 80% of the alcohol you could really reduce the amount needed for intake.. one warning i have seen on most tintitures for cannabis is be careful as its easy to take in too much since it is thc concentrate.
hope that sheds some light on it for ya.