Some colors of Fiber Reactive dye powder (pure colors which we use to mix other colors) are more difficult to dissolve than others, and if not dissolved properly, may leave undissolved dark "freckles" on the fabric. Reds especially, and they are used in many mixes including browns and grays. For solid color dyeing, especially more pastel colors, this can be particularly annoying. On the other hand, tie-dyers and painters might never notice. This is something everyone should know how to deal with, and can happen once in a while no matter where you buy your dye. Also, if you tie-dye and don't thoroughly dissolve your dye, lumps can plug up your squirt bottles, and then when you squeeze really hard, way more can pop out than you intended. Colors that require 2 or 4 times as much dye, like some of the reds, blues and blacks, are more difficult to dissolve in the small quantities of water for tie-dye, as opposed to the large quantities of water for tub dyeing.

To the rescue: UREA is your friend! It does two things. It helps dissolve more dye in less water. It also happens to be a humectant, so with tie-dye, when curing, it helps keep the fabric wet longer. This is especially helpful if you are not putting your tie-dyes in or under plastic to keep them wet. If the fabric dries, the chemical reaction between the dye and the fabric stops and you don't get optimal color.

Dharma recommends the following dye dissolving procedure:

Always add liquid to powder, not powder to liquid. (one exception, see below) Smash the powder with a sturdy spoon while adding the liquid very gradually, a tablespoon at a time. This is called "pasting" the dye. (We recommend this method even for non-problematic colors, by the way.) When it is a well-dissolved slurry, it can then be added to the dye bath or the rest of the water can be added if it is going into a tie dye squirt bottle. For hard to dissolve colors or colors where you need to dissolve a lot of dye in small amounts of liquid, use Urea water (also called Chemical Water) instead of plain water to paste up the dye. 

For mixing up a single cup of dye solution for an 8 oz squirt bottle, first dissolve 1 tablespoon urea in 8 oz of hot water. Let it cool to lukewarm, then paste up your dye with this water. This will help break up clumps and it will dissolve the dye better than plain water.

When mixing large amounts of dye or multiple colors, it is most efficient to make a large batch of Urea water.  Mix 1 cup urea to a gallon of hot water, let it cool to lukewarm before using. Also, a couple of drops of Calsolene Oil can help (breaks surface tension).  You can label and store this to have at the ready if you mix dyes often. Store in a cool place. If you open it and it smells like ammonia, it has gone bad though.

Fiber Reactive dye powders should always be dissolved in lukewarm water (like a baby bottle), not hot or cold. **If you are still having a "freckle" problem, we suggest further straining it after it’s dissolved and mixed with more water until it is very liquid, through something like thin pieces of silk (5 or 8mm Habotai works well) or fine nylon stockings placed in a funnel or strainer. Experienced dyers will tell you it is worth this little bit of time to ensure a freckle free dye job!**

Dye baths - with hard to dissolve colors, add the pasted up pre-dissolved dye to the bath, and mix well, BEFORE adding the salt. Salt reduces solubility, so if you do happen to have tiny particles of undissolved dye, they stand a better chance of going into solution without salt.

Exception to pasting up: Tie-dyers who are mixing large amounts of colors at a time for large production find pasting takes up too much time. They are putting their water or Urea water in a blender, then carefully adding the dye as the blender is going, through the hole in the top. Don't fill the blender too full, so you won't have any splashing out through that hole! If making, say, a gallon of dye, obviously the blender doesn't hold enough water. Put the total amount of dye you need in the blender with Urea water until dissolved. Then put it in your gallon container with a funnel if needed, then add the rest of the water needed to fill up your gallon jug, make sure the lid is tight, then shake. We recommending shaking your bottles before use if they have been sitting, especially with colors like black that have a lot of dye in them, as heavier component colors can settle more toward the bottom.