Someone was going to do a project on that I thought.
I wonder what became of it.
the procedure was to have an equal number of eggs from the same hens divided into two incubators, marked by date laid, hen who laid and which group.
1/2 washed and 1/2 unwashed in each incubator, each in the same room but on different plugs (different circuits).
Each incubator will need a sterile divider so when chicks hatch they cannot cross to the other side.
All eggs are handled with gloves one pair for the washed, one pair for the unwashed.
record the hatches by hen, date, and group- that is if one hen had nothing but dud eggs in both groups you could discount all of those eggs from both groups or all eggs 12 days and older failed to hatch you'll know that age matters.
Charts:
hatch by age both groups (age of egg at setting vs number hatched)
hatch by age washed
hatch by age unwashed