There is no definitive recipe for making rose petal beads. Rather than trying to give specific amounts and ingredients, I have tried to give you guidelines to follow as you do your own experimenting. In the long run, this should lead to more successful beads, as you will be able to adjust the amounts as needed since each batch of petals is different.
Rose petals: This is the only essential ingredient. All the rest are optional. You can use either fresh or dried petals. You should start with at least a double handful. If you decide to use fresh rose petals, pick the petals early in the morning when their scent is the strongest. Fresh petals make a somewhat lumpier dough than dried petals, but you can minimize this by snipping off and discarding the white "nail" at the base of each petal.
If you wish to use dried rose petals, simply spread the petals out on newspapers for several days. If you are in a hurry, you can use a convection oven with no heat to dry fresh petals, but you must cover the petals with a screen. Otherwise the blowing air with scatter the petals all over the oven.
Water: in varying amounts, depending on whether you use fresh or dried petals, and whether you "cook" the beads (see below).
Ground Orris Root: Orris root is the root of Iris florintine. It acts as a fixative which helps the beads smell stronger and stay fragrant longer. Be sure to get it in powdered form, as it is rock-hard and impossible to grind yourself.
Gum Arabic: is an adhesive, helping the rose-petal paste stick together. Get the powdered (not liquid) kind.
Flour: can be used in place of gum arabic. However, be aware that it does have some drawbacks. It has a tendency to mold, after the beads have been exposed to the body's moisture. Also, beads made with flour are more appetizing to bugs. And finally, if you are trying to get a very intense color, flour will tend to wash it out.
Gesso: (pronounced jess' -o) is a possible substitute for flour and gum arabic. I have not tried this.
Rose Oil: To add extra fragrance to the beads.
Where to Get Your Ingredients
Ideally, you will have fresh roses growing in your backyard, but let's face it, this is unreallistic for most people. Friends and neighbors may be willing to share with you, especially if you promise them some beads for their trouble. Or ask a local flower shop to save the flowers that they would otherwise throw away. You can make good use of flowers that are too wilted to be sold.
Check out gardening and herbal magazines. The ads in these can give you some leads for mail-order sources. Some cities may have herb stores, although these frequently stock only culinary herbs. Health food stores are another possibility.
Failing in that, find some potpourri made only of dried petals. You need to be aware that many brands use woody chips as filler, and these will not work.
Gesso can be found at art supply stores. They also sell gum arabic, but I have only found it in liquid form at these stores. Maybe you will have better luck.
Your first step is to grind the rose petals. This can be done either in a food processor or a mortar and pestle. Try to get the petals as finely ground as possible, as this will make the dough, and hence the beads, less lumpy.
If you are using fresh petals, you should have something resembling a paste now. For dried petals, add small amounts of water until you get a paste, or dough. If you plan to "cook" the petals (see below) you will need slightly more water here. If you accidentally add too much water, add more dry ingredients (e.g. dried petals, orris root, flour, gum arabic) until you get the consistency you want.
At this time you can also add gum arabic (or gesso or flour) as an adhesive, and ground orris root as a fixative. You can also add rose oil for scent at this time, although some people recommend waiting until the beads are formed to add it since it can evaporate quickly. I have never found this to be a problem, however.
As soon as you have a dough that can be shaped easily, you can begin to form the beads. However, the "traditional" (at least for the Victorian period) way of making beads called for the mixture to be "cooked" over very low heat in a double boiler. If you want the beads to natural colored, heat them in an enamel pot. If you wish to blacken the beads, use a cast-iron pot that has not been well seasoned (treated with oil to prevent rust). At least one recipe I have calls for adding a little salt to the mixture if you are blackening the beads. Another recipe I've seen says that the mixture can be blackened by cooking it with iron nails.
Mash the mixture against the sides of the double boiler, and let it stand over very low heat for an hour or two. Do not let the mixture cook dry. As it begins to dry out from the heat, scrape it away from the sides, stir it, and mash it against the sides again. If it starts to get too dry and crumbly, add a little bit of water. Leave it on the heat however long seems necessary to get a good paste to work with. During Victorian times, the mixture was left on the stove for five days, and the mixture was heated to just below boiling for an hour each day. This seems excessive. Several hours should suffice.
Whatever method you use, once you have a good paste that sticks together easily, you can begin forming the beads. Use a sheet of wax paper taped to the table to roll them on. Have damp paper towel standing by in case things get messy. If you want to have super-consistent beads, roll "snakes" of dough, and then carefully cut these into regularly sized pieces. Or you can simply pinch off small bits of dough for each bead, estimating the right size. Speaking of the right size, remember that the beads will shrink as they dry, so make them somewhat larger than you want the finished size.
If you didn't add rose oil earlier, you can add it now by coating your hands with it. Supposedly this will keep the dough from sticking to your fingers.
You can make a hole in the beads while the dough is still wet, although I find that it is difficult to do so without deforming the bead. Remember that the hole will shrink as the bead shrinks, so make allowances for this. I usually wait until the beads are dry (about 3 days) and then clamp each one in a small clothes pin to hold it steady as I drill a hole with a Dremel tool. Be careful if you use this approach!
You can lay your beads out on wax paper to let them dry, or you can use a strong thread and needle to string them while they are wet, and let them dry on the string. If you do this, be sure to wiggle them every so often so that they don't stick to the string. You can also form them around a long needle, and let them partially dry on the needle. Do not let them dry completely without removing them, as they will stick to the needle and you'll never get them off. The fastest way to dry the beads is to use a convection oven with no heat. The blowing air helps them to dry faster. I confess that in a fit of impatience, I have "preheated" the oven, using the lowest heat setting, but then turned it off when I put the beads inside. It worked fine, but I'm not sure that the extra heat decreased the drying time at all.
If the unthinkable happens, and the beads are a failure (i.e. crumbling and brittle), don't despair. Simply throw them back into the food processor, and fiddle with the proportions again. Think of it as a learning experience. Do not re-use beads that have gotten moldy.
Some Other Things To Try
Try other plants as well as roses. Select your materials for color as well as scent, remembering that you can always add scented oils to pretty petals. Lavender, tulips, daffodils are all possibilities, as well as various herbs. If you use herbs to make the beads, don't use the stems of the plants, as these tend to be rather woody. Use the leaves, particularly those which are lower on the stems. They tend to be "smellier."
If you know some newlyweds, offer to dry their wedding bouquets and make beads from the flowers.
Use the beads to make rosaries.
Use a mold to shape the beads. Small candy molds might work, or make your own from a clay such as FIMO.
Store your beads in a drawer or closet, and they will act as a sachet, scenting the clothes.
If the beads lose their scent (they will, eventually), you can revitalize them by rubbing rose oil on them.