Prism99

There are two basic differences between starch and sizing. (1) Starch is made from organic products -- potatoes, rice, corn, etc. Sizing is made from chemicals. (2) Starch can be made strong enough to make the fabric very stiff, whereas sizing has limited stiffening properties. This is why sizing is often used for ironing cuffs and collars -- gives a crispness without making the fabric so stiff it is uncomfortable to wear.

Personally, for quilting, I prefer starch because it can stabilize the fabric much more than sizing can. I do not like spraying fabric as I iron -- too much work for this lazy quilter. Plus, I have the beginnings of osteoarthritis in the joints of my hands (and remediated carpal tunnel syndrome); in my opinion, repeated spraying puts unnecessary stress on my hands and wrists. I think it even could result in a repetitive stress injury. This is why I limit using spray starch to preparing the top before quilting. It is also one of the reasons I do not prewash my fabrics unless necessary; the manufacturer's sizing in the fabric eliminates the need to starch the fabric. For backings, I heavily starch the fabric before sewing into a backing. For this I use a 1:1 solution of Sta-Flo liquid laundry starch and water, "paint" the solution onto the yardage with a large inexpensive wall painting brush until the fabric is saturated, wait a couple of minutes to make sure the fibers have absorbed the starch, toss in the dryer, and iron with steam.

Edit: If I wanted to make my own spray starch solution, I would simply use Sta-Flo and dilute with considerably more water. Sta-Flo contains preservatives, so the mixture should not spoil. The only thing about spraying with this (as with all spray starches) is that after spraying you need to wait a minute or so to allow the fabric fibers to absorb the starch. This is *especially* true if you are using unwashed fabric, as then the manufacturer's sizing will slow down the ability of water to penetrate the fibers. This is one of the disadvantages of using spray starch at the ironing board, in my opinion. I don't like to wait, so typically I will try to spray starch the entire area first. Starch reactivates with water so, even if it dries, a steam iron will reactivate any dried spray starch on the fabric.

Years ago I made spray starch from cornstarch (the powdered kind you use in cooking) and water. That has no preservatives in it and therefore will not keep indefinitely. I could keep it at most two weeks if I kept the spray bottle in the refrigerator; a week if left out on the ironing board. In both cases, mold would develop because of the absence of preservative.

Edit2: I do wonder if homemade Sta-Flo spray starch might clog the nozzle of a sprayer. Maybe it doesn't if made weak enough?