|No testing has came to light. If you have a pet be sure to bath them too. What your most likely experiencing is one exposure that just takes awhile to break out. The Rash may take a few days to show it self and it doesn't show itself all at once. Skin thickness and the amount of oil exposure dictate how long a certain area takes before it reacts to the oil. You were right to wash the known exposed clothing, if the oil was still present you can get reinfected each time you touch it. Shoe and shoe strings are high offenders. I hope you both are feeling better.
I like the idea of a testing light though, that seems very practical. I would think that finding oil on objects would be a simple task with such a device but the amount of oil we are talking about would be very small.