I have found that drying flowers is not an exact process and that even flowers from the same plant, produce different results depending on the time of year they are gathered.
CHOOSING YOUR FLOWERS
Choose perfect blooms where possible, as drying tends to accentuate imperfections. Gather your flowers late morning, when they are dry, but not yet wilted by the heat of the day.
Orange, pink and blue flowers tend to retain their colour best when dried, red roses darken considerably but are still very lovely.
If you are not able to start drying your flowers immediately after picking, keep them in vases of tepid water in a cool place until you are ready. I have found that drying flowers that are beginning to wilt produces disappointing results.
HOW TO USE SILICA GEL
The best results are obtained by using generous amounts of Silica Gel.
Use an air-tight container made of plastic, glass or tin. Pour a 3cm layer of Silica Gel into the container and then arrange the flowers face up on this layer, the next step is to cover the flowers completely with Silica Gel.
It is important that this is done carefully, as simply pouring the crystals onto the blooms will flatten them. I have found that the best way to do this is to pour the Silica Gel around the edge of the container, then shake it gently so that it moves to the centre of the container, building up around the flowers and filling up the spaces between the petals, until the flowers are completely covered.
It takes between two days and a week for flowers to dry, the length of time depends entirely on the type of flower you are drying, and I have discovered the best results are obtained by only drying one type of flower per container as those with thick fleshy petals will take longer to dry than those with thin papery petals.
It is important to regularly check the state of the flowers, because if they are left too long in the Silica Gel, they will become brittle and the petals will break.
Once your flowers are dry, remove them gently from the Silica Gel, either by hand or using a slotted spoon, and remove any residual crystals with a soft water-colour brush.
USING SILICA GEL IN YOUR MICRO-WAVE OVEN
The drying time for flowers can be reduced dramatically by drying them in a micro-wave oven. This technique is very tricky in that it requires split second timing otherwise one tends to end up with cooked flowers.
The method is essentially the same, but it is better to dry only a few flowers at a time.
Once you have covered the flowers with Silica Gel, micro-wave them on high for one minute and then let them cool undisturbed for 30 minutes, check that the flowers have dried and if not repeat the process. Here again I am unable to give you exact instructions, as drying using this method depends on the type of flower being dried, and the power of your micro-wave oven.