Add the grapes and blackberries to a food processor, chopper, blender. I used the Ninja and it really makes a smooth job of this process. Here is a link to the exact one that I have Ninja Master Blender
After the fruit is all blended put through a sieve.
I like the clear fruit juice.
I also rub my finger around in the sieve and get as much juice as I can.
There will be pulp leftover when you are done.
Do not worry about exact measurements.
Pour into your popsicle molds, stick in your popsicle sticks and freeze at least 6 hours.
Here is the clickable link for the popsicle mold that I used. I have used it a few times now and it works really well. Ice Pop Maker
To get the popsicles out of the mold I ran hot water on the underside first.
Take the frozen popsicles out of the mold and put in a freezer bag.