For example: we immerse without bracha on utensils made of porcelain, but utensils made of glass we do immerse with bracha. If I don't know if it's actually made of glass or porcelain, what should I do?
There is a general principle that when there is a doubt over which blessing to say, we take the lenient view; that is ספק ברכות להקל.
This derives from the fact that blessings are Rabbinic in origin and we take a lenient view when there are doubts in a Rabbinic "situation"; that is called ספיקא דרבנן לקולא.
If the blessing were made and it would have been inappropriate we would have transgressed the principle of אסור לברך ברכה לבטלה - it is forbidden to make a blessing for no purpose.
This is all explained in "Pninei Halocho" of Rabbi Eliezer Melamed.
So if in doubt (and you do not have a vessel to immerse that requires a blessing to immerse first), immerse the vessel without a blessing.