Try about a 1/4 of a cup of the Peroxide, along with your normal dose of good detergent. The warmer the water, the better, but not necessarily 140 degrees. Again, it will most likely take numerous washes to release all of the grayness. I do laundry for my aunt, who has tons of nylon and other synthetic materials. Over the past year or so, I have managed to get them all white again, after years and years of cold/cool washes and cheap detergent. It will take time, patience, and trial and error. If you truly love the garments, then it is worth the time and effort, IMHO.

The adjustment for bobbin tension is located on the bobbin case. If you look at the bobbin case you will see a small, tongue-like piece of metal that is held in place by one or two teeny-weeny screws. When you put the bobbin in the bobbin case you pull the thread under that tongue before inserting the case in the race mechanism. Your machine should have the very fine screwdriver required to adjust the screw. Look to see if you have it and haul out the manual for a quick "looky-see" for advice. Bobbin tension is a routine part of working with your machine and anyone who tells you NEVER TOUCH THE BOBBIN TENSION knows very little about sewing. True, you should go racing for it, but when working with very thick materials it can be a real help to know how. It's one more arrow in your quiver of alternatives, that's all. A tip: lay down a pale pillow case and work over that. It's really easy to loosen the screw too much and have it fall out, on a large flat area with a pale background you're less likely to LOSE the screw, you guys. I learned that one the hard way, lol. When adjusting the bobbin remember that a little goes a long way! I start with a quarter turn and then do a stitch test. You have to be patient and methodical. Another good test is to put the bobbin in the case, hold onto the thread and see if the case falls away in a steady, controlled way. It shouldn't hang there (too tight) nor should it fall rapidly down (too loose). Get out those manuals and fiddle around, ladies. You really have nothing to lose by trying. There is always a mechanic to bail you out and don't be afraid to ask questions and have him/her SHOW YOU. This is what you're paying for, afterall. 1.) is the machine clean and oiled? 2.) is the proper size needle inserted properly and without burrs? 3.) is the machine threaded properly? 4.) have you checked the tension adjustments with a stitch test?

"Before I was a "real" quilter, I used sheets to back my quilts. I also used hospital blankets as batting. Boy, did that make them heavy. I just tied quilts then, no stitch quilting. Some of those monsters are still floating around." Exactly, and when I make an utilitarian anything, I always try to use up something to recycle it. My very first puff quilt was made with a motley assortment of fabrics, many of them old sheets. I have had it three years now on the daybed in the living room. It gets lolled on by gardeners with boots on, the dog and cats, it gets thrown in a washer at least one a month, and still is going strong, and just beginning to show some wear. IOW, my biggest investment was time and it has outlived anything I could have purchased commercially and manhandled like that. My ex MIL was the first quilter I ever met. She produced dozens and dozens of them over the years, made of old coats, men's trousers, sheets, wool blankets and backed with feed sacks. She is dead now, but her quilts are still on family beds four decades later. I can't think of a definition of a 'real' quilter as applied to fabrics. It's a folk art form and you are free to express it however it works for yourself. You may not be free to enter such a homespun creation into a show, but I've seen some of those old jewels made of things handy in exhibitions, and antique stores. I do frequent fabric shops now for 'quilter's cottons' and use them for things I do in this forum millieu, but I still do my primitives for my own use and gobbling up fabrics and reusing them are a fun way for me to express myself in a manner I can afford, and feel good about 'being green'.

We are going through this with the Kivik right now. We had one with a white cotton cover but it was destroyed in the great fire/flood of '15. We went to replace it and found the white cover was quite different. I haven't tried to wash it yet, but I've noticed it catches grime much easier than the old cotton one. My DDs go to private school and wear white shirts. The old uniform shirts were cotton and you could get the stains out, but they were replaced with poly shirts that hold onto stains, so I'm not hopeful that the new poly Kivik cover will fare any better. It also doesn't feel as nice, but all the rest of our soft furnishings are natural fabrics, so I'm a bit biased.