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General procedure (shown for red cabbage): Cut sample in small pieces, then extract dye in warm water (or ethanol) and filter it.
pH INDICATORS FROM FRUITS, VEGETABLES, FLOWERS, ...
-----------------------  RED CABBAGE :
---------------  CHERRIES :
-------------------------------  POPPIES :
----------------  PANSIES :
-----------------------  ELDERBERRIES :
-------------------  ROSES :
A pan with hot water and red cabbage!
------------  MALLOW FLOWERS :
-  BLACK CURRANT :
---------------------  BLACKBERRIES :

 ----------  HORTENSIA :
-------------------------  CUCURMIN ::
Cutting SOME of the cabbage in pieces and add it to hot water.
-----  RHODODENDRA :
Colours of red cabbage water extract (aka pH indicator) with different household materials:
distilled washing vinegar (left, acidic) to stong soap (right, basic).
Colours of red cabbage water extract (aka pH indicator) at different pH: from very acidic (pH 2, left) till very basic (pH 11, right). Creative Commons Attribution- Share Alike 3.0 Unported license (Wikipedia)