7.5 kilos of blackberries have become jelly or jam recently
re pans Al is a bad idea, copper is fairly ok for most things so long as it is shiny when you start ( any copper salts on the surface of the metal will end up in the food so polish before use ), tinned copper i would avoid but decent stainless is hard to beat.
shape matters as well, some heat sources are suited to round based pans , some flat.
whichever, wide and big is good for jam to allow for frothing and if needs be evaporation
the pan needs to be at least twice as big as what you pop into it