Use Or in your portal filter so that you can filter when one field is empty and the other not:
( IsEmpty ( Global::Material ) And PatternCount ( Portal::Description ; Global::Description ) ) or
( PatternCount ( Portal::Description ; global::Description ) And Patterncount ( Portal::Material ; global::material ) ) or
(IsEmpty ( Global::Description ) and Patterncount ( Portal::Material ; Global::Material ) )
You might be interested in the search portal examples found here: https://www.dropbox.com/s/0pm1gdqcfi2ndpv/EnhancedValueSelection.fp7
They update keystroke by keystroke and do not use RefreshWindow to get the portal to update as the data used in the filter changes.
(FileMaker 12 and newer users can use Open from FileMaker's File menu to produce a copy of this file converted to the newer file format.)