What's the reason behind urushi colors?
While I'm still working on my first synthetic kintsugi, I'm reading up on traditional methods for the future.
It seems that at different stages the urushi is mixed with different powders (iron oxide for black and clay for red). I'm wondering is there a reason for it?
Of course, one of the reason would be visibility. You can see where you have or have not applied the new layer, but I wonder if urushi properties change with each mix?
I'd assume that raw urushi would be the most "sticky" so that's why it's used first. Adding iron oxide would thicken it to make it easier to brush on perhaps? Maybe is has another quality that I'm not seeing? What about red? Would it mixing clay make the finish closer to ceramic? Does it make it food safe?
I'm just curious if there's science behind the tradition.