When blending for a specific yarn or knitted fabric, special attention must be paid to whether or not it will destroy the integrity of the fiber. [This is actually a complex question that has been answered in different ways by numerous people. In no way do I profess to have all the answers to what happens when fibers are blended.]
In general, temperamental fibers should only be blended if they are non-superwash treated Merinos, or if you know for sure that they won’t mind being mixed with other types of wool! The main thing about blending fibers is to make sure you don’t mix them while they’re still wet from washing and rinsing because this can lead the fiber to felt , which effectively destroys its strength and usability.
Simply put, blending is mixing different types of fiber together. There are two main reasons for blending fibers: to create a novelty yarn , or to ‘stretch’ your stash by using up small amounts of leftover bits and pieces. Yes, you can blend fibers before washing them, but I recommend that you first wash the fibers very carefully by hand to ensure they’re not carrying any dirt or other contaminants.
Washing the blended fiber will allow you to see exactly what you have so that it can be divided into its parts for spinning . On the plus side, washing the blended fiber gives it a chance to relax and settle with one another after being jostled during transport and storage.
Nature abhors chaos! After you’ve blended your fibers, washed them, and allowed them to dry completely , you can begin to spin the blend. Just don’t try anything too fancy at this point because of all the lumps and tangles .
The end result is a bit like Frankenstein’s monster, but that’s what novelty yarns are all about! The big advantage (and surprise!) that comes with blending fiber before spinning it is that there are no limits on what kinds of fiber you can combine in one yarn. There really aren’t any rules here; I like to experiment with whatever happens to be sitting in my stash or whatever looks good when I’m browsing through my local fiber shop (yes, this actually happens!). I especially love blending fuzzy wools with sleek mohairs or shiny silk, or playing around with different textures. It’s a very satisfying way to use up small amounts of fiber that are left over from other projects.https://thejuicerking.com/does-blending-destroy-nutrients/
I think some people are under the impression that blending destroys all those special qualities that each individual type of fiber has – namely that the fuzzies get lost in the sleekness and that the shiny gets absorbed by the matte.
This can be true if you’re using a really extreme fiber to blend with, but it’s also possible to create gorgeous blends that look even more amazing than their individual components. The reason is because there are different types of blending going on:
Blending for color transition :
In this case, each type of fiber contributes a couple of colors which make up a larger range when blended together. For example, imagine wool and mohair were used in equal amounts to create a blend; one would contribute orange tones while the other contributes green tones, creating an overall “earthiness” when put together.
Another example might be silky mohair combined with roving wool; the mohair would contribute a shine to the fabric while the wool provides bulk. The result? A blend that has more texture than smooth silky yarn, but is shiny and has lots of drape.
Blending for color accuracy :
Sometimes you’ll want to create an impressionistic color scheme with various fibers’ colors combined together in one yarn so it truly looks like “mood ring” when knit up — who doesn’t love all those vibrant colors?! This works especially well if you’re using dyed rovings & handspun yarns since some of their depth can be lost in a blend.
Have some bright pink alpaca roving from your favorite spinner? Add in some deep purple merino/tussah silk/mohair laceweight to give your variegated colors more depth. You can also use blends for colorwork or stranded knitting – one color is usually heavier than the other, which allows the knitter to create designs within a yarn & not have to switch balls/skeins mid-point.
Blending for different fiber properties :
Some animals’ fiber comes with various degrees of crimp that you simply don’t see when using just one fiber type. A blend could be used to simulate this if it’s what you’re looking for in a knitted fabric (i.e., super soft wool with some bounce and loft but not necessarily dramatic stitch definition).
If you like the of working with “exotic” fibers, a blended yarn may be a good choice for you. Blending for higher quality : Sometimes a mill will blend together wool from multiple sheep breeds or colors to create a finer yarn that would be pricier if all the fiber came from just one breed/source.
The result is usually called a “Romney,”  or “merino-based”  yarn – but there are different kinds of blending & it isn’t always easy to figure out what the final product might look like when shopping!