Performing a filling is the most scaring moment of making Irish crochet lace. In modern version of this lace, we use a lot of irregular filling, and here is a small video on making it.
Of course there are many patterns for it, but I prefer the "soil crust", that resembles a texture of the soil, that was dried out by sun. Probably because I see it 6 month a year, it is more natural to me.
