Wooden floorboard draught proofing question

Hello! First post here!

We are decorating our dining room and decided it would be nice to expose the old wooden floor.

After ripping up the carpet and inspecting the floor it seems to be in great condition which was our biggest worry.

My query is that the gaps between the floorboards appear to with something (not sure what) which over time has fallen out in places.. (see attached pic).

What is the general consensus for draught proofing when you are faced with something like this? I've been looking at old pine silvers and draughtex as a solution but neither seem like they would work.

I've also had a go at tapping out what ever has been used but it seems fairly durable and takes AGES to do a small area.

Any suggestions would be appreciated

Paper Mache with some suitable colourant added works well, costs little and is probably what's bean used already, so you only need do the missing bits...pinenot