You may have heard that dye lots don’t matter because everything is computerized now. It is not true. Dye lots matter! There are quite a few factors in how the yarn takes up the dye, so even when exactly the same formulation is used the colour will change slightly ( or drastically) between dye lots.
When yarn is dyed, there are many things that will affect how the dye is taken up by the yarn.
First of all if the yarn is an natural fibre, the amount of sun the animal or plant was exposed to will affect the colour of the fibre. Just as our hair gets lighter in the sun so too do animal fibres. If the season was a rainy season the fibre will be darker than if it was a sunny season. The slight variation in colour in the base yarn will also show up in the dyed yarn.
The temperature of the water in the dye bath as well as how long the yarn stays in the dye bath will also affect the colour of the yarn. The longer and the hotter the water the more dye wil taken up by the fibre affecting the final colour of the yarn.
The amount of moisture in the fibre will also affect how much dye is taken up. The dryer the fibre the more dye that will be absorbed. The more dye taken up the more intense the colour.
Below is a picture of 3 different dye lots of the the same colour on the same yarn base. This is a more extreme variation than what is normally seen, but it illustrates how different dye lots can be.
3 Different dye lots of Biscotte and Cie Bis Sock in Apple Core.
The moral of the story is to buy enough yarn for your project and check that they are all of the same dye lot. Even better buy 1 extra just in case and if you don’t need it for your project bring it back and exchange it for another ball of yarn for your new project.