Blackberry colour changes

Last year we had fun picking blackberries and making jam, so I thought we could do it again.  This time my son wasn't so keen on the actual picking after an unfortunate incident with a patch of nettles, but he was still pretty enthusiastic about eating them and making jam!  We made one jar of jam, which the small boy is enjoying eating on toast.  I also thought we could experiment with whether the blackberries would give a pH-dependent colour change like red cabbage, poinsettia or blueberries.

Sieve with blackberry seeds

We made the jam seed-free by straining the boiled blackberries through a sieve, which leaves a bit of blackberry puree on the sieve.  We used the sieve to 'paint' some sheets of paper with this thick blackberry liquid and left it to dry, with it changing from a red to a deeper purple colour.

Painting with vinegar and bicarbonate of soda

To test the colour changes, I gave my son a little white vinegar and a small amount of bicarbonate of soda dissolved in water plus two paint brushes, and asked him to see what happened when he painted the blackberry puree-covered paper.  He discovered that he could make it turn bright pink with the vinegar and dark blue with the bicarb - the colour changes were more intense than I've ever seen with red cabbage on paper, probably because the blackberry was much more concentrated than we've achieved with red cabbage cooking liquid.  

Making pictures disappear

My son spent a while painting with the different colours then making them disappear.  I managed to sneak in a little practice with letter formation by painting letters of the alphabet with bicarb then getting him to erase them by painting over the letters with vinegar!  I've put a few more photos of this on my Instagram account.

A couple of days later

What we've discovered since is that over the course of around 24 hours, the acid bleaches the colour so that it turns almost white, and the alkaline patches go a darker blue, almost black!