Washed & Unwashed
 

It could. Some fabric doesn't shrink at all, other fabric can shrink a lot. Also some fabric is more color fast than other fabric. Don't know what to suggest for you and the mixing them. I wash all my fabric and iron it when I'm ready to use it. That is why I don't do fabric swaps - don't have any control over what others do.

You can mix washed and unwashed in the same quilt top, but you need to be aware of a couple of things.

Once quilted moderately, the batting will control shrinkage so variations in shrinkage of fabric are really not an issue. (It *is* an issue if quilting lines are far apart -- say more than 6" -- or if a quilt is tied; then you would not want to mix washed and unwashed.)

To prevent possible bleeds from settling into other fabrics, it's a really good idea to wash the finished quilt with Synthrapol in a machine that uses a *lot* of water. Synthrapol suspends dye particles in the water so they are rinsed away. You need a washing machine that uses a lot of water so that any bleeds are diluted enough. Domestic front loaders don't use enough water for Synthrapol to be effective; however, domestic top loaders and laundromat front loaders are fine.

I mix washed and unwashed all the time. The advice Prism99 gave you is great.

I'd guess that it isn't going to be make a big difference unless you are working with large pieces or denim. Denim tends to shrink a lot--but if you wait until after you finish it to quilt it, things will be better. Usually 1 spy pieces are pretty small--5 or 6"--I think you are fine.

if it is a swap, you really should abide by the swap rules. If it is for yourself, I never prewash and find that after it is quilted, moderately to very close together, there is minimal shrinkage.

If you do a swap then one needs to follow the swap rules. If you don't agree with the washed or unwashed then don't do the swap. Unless, you are prepared to wash the fabri you get and take a chance of bleading or shrinkage and prepared to recut the pieces (that is if you get small pieces. fat quarters are not necessarily a problem.

I do not pre-wash, but have been given fabric that was. Have used everything together, and don't give it a second thought. As Prism99 said, the amount of quilting will help.

I prewash, but it is really up to you.

Thank you all for all the answers, it sounds like it will be ok to mix them. The first swaps were for 4" squares and now I want to switch to 5" squares.
I do abide with what ever the swap says, that wasn't the question. If it says to wash, I wash, if it says not to, I don't.My concern was mixing the two.
Thanks again for all the help.
Linda