and with a happy degree of success!
I recently made 2 batches of baking soda clay:
The first one used a surprise find at the Mix Markt in Betzingen: a 500 gr. box of Natriumhydrogencarbonat (only 55 cents (€)!). The Mix Markt carries a line of products largely from Russia and eastern Europe and they have 100 stores throughout Germany, so hopefully you German followers can find one.
The other batch I made with Natron, purchased at the cost of 1 kilo for 2.31€ from Lebensmittel.de but they charged a whopping shipping cost of 4.90€! Never again will I do that for a lone purchase!
In any case, both batches turned out just beautifully! (Oh, I did try some very cheap Waschsoda at one point but although my hands got very clean it did not ever produce a working clay consistency.)
Then I divided the cheapie batch to try out the various dyes I have. Yellow was the winning color and I used
4 drops of McCormack's liquid food coloring in one batch,
two small blobs of AmeriColor's gel food coloring in the second batch
and a tiny pinch of powdered German Lebensmittelfarbe from Birkmann in the third batch.
In each case I kneaded in the coloring and, although each a different shade, they are all quite pretty.
heart ornaments were much better.