We forget. We forget where we put our crochet hook. We forget where we bought that lovely, unusual ball of yarn. We forget the importance of dye lots. Recently someone approached me in a yarn shop for help selecting yarn for a project. Despite the person having experience working with yarn, to my surprise, they had no idea what a dye lot was. This is a problem and here's why...
Q: What's a dye lot?
You may not have noticed that yarn balls have dye lots. When yarn is dyed, it's done in batches, or lots. And, no two batches come out exactly the same. It's just like baking; no matter how hard you try, the recipe is going to come out slightly different each time you make it due to subtle differences in the ingredients themselves and the amount of each ingredient used. This means that, when dying yarn, the colour achieved during the dye process will vary with each and every dye batch. So beware! When starting a crochet project, especially those that require several balls of yarn (say a sweater or a blanket), you need to buy yarn balls that share the same dye lot to ensure consistent colour. If necessary, this means that you want to buy more balls than needed and return the extras to the store for refund (check before purchase if this will be possible) once your project is finished. Otherwise you may not be able to buy more yarn from the dye lot you need. If this happens, you'll be forced to finish your project using balls of yarn from different dye lots which have subtly different hues. This means that your final project could have patches or "stripes" of different colours visible where you don't want them (like the image for this post above).
It's also really important to note that, even when dye lots do exist, the colour of the yarn may not be totally consistent or uniform throughout a ball or from ball-to-ball. This is especially true of natural fibre yarn such as cotton or wool which is hand-dyed. Not only will there be variation in the quality of the natural fibre—perhaps there is more lanolin (natural oil in sheep's wool) or fine twigs/dirt included—but also possible variation in how the yarn itself is spun (the looseness or tightness) and even the dye bath temperature, which will cause the dye to be absorbed differently throughout the full yarn length. I always advise that you look at all yarn balls before purchase in bright, preferably natural, light to see if the colour is consistent. Believe me, it can save you lots (pardon the pun) of future grief.
For more tips on keeping the colour of your project consistent, check out Should I Alternate Skeins? Yes, And Here's Why on skeinyarn.com.
Happy yarn shopping!