We cardmakers are all well aware of how much of a challenge working with vellum can be.
Its translucence is the single thing that poses the biggest problem in that almost nothing works when trying to adhere the vellum to another surface. In my experience, I have never come upon a product that doesn't show through the vellum, even adhesives that are meant specifically for use with vellum.
That's why I always welcome any tricks I come across for the adherence of this fussy component.
Recently, putting together a card from an old Stampin' Up! kit gave me just such a wonderful solution.