What is a dye lot, and how to use different dye lots of the same yarn
Yarn made of synthetic fibers is dyed as the fiber is produced. The producer uses chemical dyes so the yarn has the same dye lot through out production. Therefore, when you look at the yarn wrapper you will find "No dye lot" printed on it. With this kind of yarn, you do not need to worry about different shades.
On the other hand, yarn made of natural fibers usually is dyed in large batches and each batch has its own number. A little disparity in the amount of dye used in the batch, will cause a different dye lot or shade. When you buy yarn, make sure you have the same dye lot; otherwise, you may end up with a slightly different shade of the same color. Dye lots are represented with a number on the yarn wrapper. If you match the dye lot numbers, you should have the same shade yarn.
However, sometimes due to human error you may find different shades with the same dye lot number. If the yarn is exposed to direct sunlight, it may fade and you will end up with different shades in the same ball. Other times, you may not be able to find the same dye lot of the yarn. In such circumstances, there are several ways to remedy the problem: