I cook marmalade on agar-agar (I buy agar via the Internet). This marmalade is dense to the touch (convenient for slicing), while it tastes soft, does not stick to the teeth, does not look like a dense jelly (different structure). And, importantly, it is easy to prepare. I usually make marmalade from currant juice (and even cherries, cranberries. Berries are both fresh and frozen).