Many of the old texts refer to soap, or "soaping up". This appears usually in the context of setting creases. For example in Delafera's The Art of Garment Making it's used in reference to creasing the quilting lines in silk facings of smoking jackets.
I have struggled to find much contemporary discussion of tailors soap. It is sold by The Lining Company, and the Caffeinated Tailor on YouTube uses soap (a generic brand Lagarto) when making up waistbands. Is this something others have experimented with and is it still relevant in today's tailoring?
Do you apply this to the inside of the crease ort the outside...?
I work wiht a lot of very heavy cloth and getting creases that stay is a big problem. I have just bought 102m of varius hand woven Harris Tweed roll ends and it it LOVELY but the crease lasts about 4 hours...