Please do not make this if you are under age and without parental supervision. My mother was present through out.
The plan is to steep them both in vodka or another dark liqueur. Which ever is cheapest. The blackberries contain sugar and vanilla essence. The rhubarb has cloves, cassia bark as I had no cinnamon.
Popping into a cold dark place for occasional inversion.
My thanks to @bobleponge216 and @haywayne and @notjustjams for their advice.