Welcome to SMF,
@soapexperiment !
I like this idea!
In essence, you are only changing the water content of the soap batter. In theory, the final soaps (after prolonged cure) should be identical, but in practice, you will without doubt notice differences. I bet that quite a few people would be thrilled about such a systematic experiment.
From the perspective of a soapmaking practitioner, a major thing that is influenced by lye concentration (but not necessarily noticeable in the final soap) is
speed in the sense of
time to trace, i. e. how much time and/or mechanical torture (stick-blending) it takes for the lye and the oils to combine into a smooth, thick batter.
There is a situation during the saponification that is called
gel phase where the soap has a vaseline-like look and consistency. It is well-known that
forcing and
avoiding gel phase is controlled, besides temperature, by lye concentration. Although the final soap (final = after >6 weeks cure) isn't so much different, it
looks different. Have a look at Auntie Clara's blog seriers about the
Ghost Swirl Ghost Swirl Soap Archives - Auntie Clara's Handcrafted Cosmetics that exploits (and explains) these differences for a visual effect.
Note that ghost swirl, glycerin rivers, etc. are effects that do not depend on the chemical composition of the soap, but the way that the soap molecules are arranged within the microstructure (ordered or clumped, crystalline or random). This has not so much to do with traditional chemistry, hence the preferred analysis techniques are likely microscopy, X-ray diffraction, or NMR. If you haven't made gross mistakes, pH is one of the
less interesting parameters to measure in soap.