Originally Posted by Doctor Shinobi
now about the sealing... is that really necessary to buy these products? i could just wet the fabric with water and a brush to make sure the fire doesn't go beyond where i want it to go.
I don't think you're fully understanding, so maybe I can clarify a little.
First, if you already have your fabric for this scarf, use a swatch of it in a burn test. You need to see how the fabric reacts to flame. Will it even burn? If so, how does it burn? Different textiles burn in different ways. Silk and cotton burn very readily and will turn to ash (and in different ways). Polyester, on the other hand, is more resistant to flame, and it does not turn to ash.
Polyester is basically a plastic fiber - it does not burn, it melts. Have you ever thrown a plastic Dixie cup into a bonfire before? (If not, I highly recommend it sometime. It's very entertaining.) It just stands there in the fire for a few seconds, then it suddenly wobbles and melts into a puddle of colored goo. A paper cup, on the other hand, will catch fire and leave ash behind. Same idea with synthetic vs natural fibers.
Now, for the other half of this equation: fabric unravels. This is why we need to hem garments, finish our fabric edges, or seal the fabric, otherwise the garment will fall apart over time. So, if you don't want your scarf to keep unraveling and losing fibers after you've cut and burned it, you need to make sure the edges are all sealed.
If you burn polyester or polyester blends, the polyester content leaves a melted edge behind. This means that if you put it to flame, the edge will be sealed at the same time, stopping the fabric from unraveling. It's a two-in-one process.
If you burn natural fibers, the edge is -not- self-sealing. The edge will be flaky ash and the fibers could still continue to unravel. This is where you'd need a sealing agent like Fray Block. You would apply it AFTER you've done all your burning to preserve your work.
Do not try to use Fray Block to control the flame, and do not burn fabric after applying it. It is flammable. You may end up with toxic fumes or a fireball in your face.