Way back when the dinosaurs walked the earth (1950's) - I remember ironing starched items - that had been treated like EasyPeezy stated - and the iron never ever got gunky.
I think Mom used Argo starch with a bit of Satina added to it. It started out with cold water and the starch mixed in the bread bowl, and then she added boiling hot water to it, Then that little blue waxy piece was added and stirred in to the mixture until it melted.