Although silk is a natural, organic fabric, it has long been thought of as a difficult fabric to maintain and clean. That is not necessarily true, particularly regarding newer silks. Successfully changing the colour of a dress or other garment by using fabric dyes is possible when the correct dye, procedure and precautions are utilised.
Select your new colour, keeping in mind that the original, underlying dress colour will have an influence on the end colour. In other words, a red dress dyed with a blue dye will have a purple tone. A yellow dress dyed in a blue bath will become green. Also note that, in many cases, the thread used to sew the garment is not silk, but a synthetic. Non-silk threads and zippers may dye either a lighter colour or not at all. If that is the case, your newly dyed dress will be "accented" with the original coloured thread.
Before preparing the dye bath, read and understand the instructions on the dye package thoroughly. Make sure you have enough dye packets to accomplish the colour you desire. The general rule is one packet for every one pound of cloth. The more dye in the bath, the more intense the colour. Also, do not ignore the need for a mordant additive to the dye bath. Different colours require different additives. A mordant is added to set or fix dyes on fabrics by forming an insoluble compound with the dye.
Fill the pot with enough water that the dress will be able to move freely. Heat the water to just below boiling. While the water is heating, thoroughly wet the dress in warm water. When the water is almost boiling, add the dye packet(s) and mordant. Stir with the large spoon until you are sure all the dye and mordant is dissolved.
Add the thoroughly wet dress to the dye bath, making sure all parts of the dress are submerged. Stir the dress in the dye bath frequently and maintain the water temperature at just below boiling. Although silk absorbs dye rather quickly, the longer the dress is in the dye bath, the more intense the colour will ultimately be. Twenty minutes to a half hour in the bath is a general guideline. Remember that a wet fabric colour will appear several shades darker than when it is dried. Also note that a dress has seams, pockets and other areas where the dye can "hide" and become more intense in colour than the rest of the dress. Proper agitating of the dress in the dye bath--followed by repeated rinsing of all areas of the dress--can prevent this.
Carefully remove the dress from the dye bath with the spoon or tongs and place it in a sink or tub of clean warm water. You may want to have a large bowl handy to hold under the dress to catch any drips as you transfer to the first rinse bath. Gently swish or agitate the dress in the rinse water. Drain the water and repeat until the water no longer shows any dye colour. This may take several rinsings. The final rinse should be in cool to cold water. As an alternative to the final rinse, you may use the rinse cycle of your washing machine. Be advised that using this method is tougher on your dress and fabric because of the agitation of the washer and you will need to clean the washing machine when you are done with one or two cycles of bleach and water.
Carefully hang the dress to dry. Never use the dryer, and avoid hanging it in direct sunlight. Once the dress is dry, you may steam-press it or send it to the dry cleaners for professional pressing.
Fabric dyes are non-toxic and easily disposed of down the drain. Should the dye colour a counter top or sink, a mild solution of bleach and water should clean it up.
There are no guarantees when you are dyeing any garment, whether it is made of silk, cotton or another material. Therefore, before you begin, understand that that the dress may be ruined by the dyeing process. Then, again, the dress could turn out more dazzling than it was originally!