How the radiocarbon date work in case of quran dating?

How the radiocarbon date actually work?The sana manuscript has 2 layer text,how they dated these 2 layer texts aka upper and lower text?I heard carbon dating can only date the material itself, the paper or parchment, not media used to add content to the parchment or paper substrate.So how actually they dated it?Can they date the ink of the text or not? If they can then why they aren't be sure about the date of birmingham manuscript?In the case of Birmingham manuscript, it has its verse ending dotted,even the chapters endings are dotted and it was not early quranic style so even though I believe that it first century manuscript but It's so early date is not believable, but if they can date the ink, the dating can come more accurate may be,So can anyone tell me how they carbonated sana manuscript?