These Diamond Gem Cookies are dipped in a blue watercolor glaze and accented with royal icing details that are sprinkled with sanding sugar or painted with edible gold luster dust. They are great for a Gemstone Birthday Party!
For my oldest daughter's 12th birthday, she wanted a Geode and Gemstone themed party with shades of blue since blue is her favorite color.
We though some diamond shaped cookies would look really pretty.
I decided to use the method I developed for these Snowflake Cookies, which consists of a simple, soft cookie glaze and minimal royal icing details. This keeps the overall cookie softer and easier to bite than cookies fully covered in royal icing. I later used this method for Easy Polar Bear Cookies as well.
Rather than a solid color glaze, I covered the cookies with a marbled glaze to add some visual interest.
I used the royal icing to define the shape and facets of the diamonds. To provide some variation, I covered the royal icing with either white or blue sanding sugar or painted it with an edible gold luster dust suspension.
My daughter and her friends loved how these turned out!
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Supplies
- 1 batch roll out shortbread or sugar cookies
- Cookie glaze (from Iced Vanilla Shortbread Cookies)
- Blue food coloring liquid
- Easy Royal icing (will require meringue powder)
- White and blue sparkly sanding sugar
- Edible gold luster dust (recommended: Truly Mad Plastics)
- Everclear, vodka or clear extract
- Plastic disposable transfer pipette
- Food grade paintbrush
- Food dedicated paint palette
- Disposable piping bags
- #2 round tip, optional
- Plastic piping bag tip coupler, optional
Cookie Base
First, you need to choose a cookie base for these cookies. It needs to be a lighter color dough in order for the pastel glaze to maintain the color.
I used Vanilla Shortbread Cookies, but my Cut Out Sugar Cookies would also work.
Roll the dough to an even thickness. I use wooden dowel rods as guides to roll the dough evenly.
Cut the dough with a sharp paring knife into diamond shapes of different sizes. It is basically a triangle with two corners (vertices) cut off.
Bake the cookies according to your recipe's instructions, and allow them to cool completely before glazing.
Glaze the Cookies
Stir together the glaze ingredients. Add a small amount of liquid blue food coloring to the glaze and swirl it with a toothpick. Be careful to just add a small amount of coloring. This is why I recommend using a liquid food coloring instead of a gel, as the gels tend to be very intense color.
Place one cookie face down in the glaze and dip it. Then, lift it out of the glaze, let the glaze run off of the cookie and place it on a rack to allow the glaze to set. This creates a marbled or watercolor look.
Repeat with all of the cookies. Allow the icing glaze to dry at room temperature until set, at least a few hours.
If you want to allow them to dry overnight, place them in a single layer in an airtight container after the icing has partially set.
Royal Icing Details
To add the royal icing details, start by mixing up the Easy Royal Icing stock using meringue powder. Then, add about a half cup of the base icing to a small bowl. Add small amounts of warm water to the icing to thin it slightly so it is a pipeable consistency through an opening the size of a #2 size round tip.
Transfer the icing into a disposable piping bag fitted with a #2 tip. A tip coupler is helpful for securing the tip on the bag. It also allows you easily to switch tips if the #2 tip is too small and you want to bump it up to a #3 or even a #5.
Alternatively, you can cut off a very small opening in the tip of a disposable piping bag. Start with a small opening because you can always cut a little more to make the opening larger if it is too small.
Locate the sanding sugars so you can use them immediately after piping the icing. Depending on the temperature and humidity of your kitchen, the icing can set quickly so you want to get the sugar on immediately.
Before piping the details, it is important to go over some basics of diamond anatomy. I have included this image from Kim Quang Jewelry that I edited to show the relevant parts for the purposes of these cookies.
The diamond consists of top crown separated from a bottom pavilion by a girdle. The bottom point is called a culet. The lines on the crown and pavilion represent the facets on the surface of the diamond.
Start by piping an outline around the diamond shape.
Then, pipe a line across the cookie to create the girdle of the diamond. The girdle separates the crown of the diamond (top) from the pavilion (bottom).
Next, pipe a zigzag line across the crown to give the illusion of facets.
Last, pipe two lines down across the pavilion that connect the girdle to the bottom point (culet), creating the illusion of facets on the pavilion.
If you are adding sanding sugar, immediately sprinkle it over the whole cookie, specifically over the royal icing, then shake off the excess sugar into a small bowl. This will allow you to reuse the sugar that does not stick to the cookie.
Set the cookie aside on a baking rack to allow the icing to dry. Repeat the royal icing piping with the remaining cookies. Leave some cookies without sanding sugar to paint with edible gold after the icing has fully dried.
Because you are working quickly and doing only 1 cookie at a time, you may need to cap off your piping tip between cookies or place the tip in a tall glass with a moist paper towel in the bottom. This should help prevent the icing from crusting over the tip.
Make sure to check your tip for crusting each time before you begin piping the design. Sometimes, I will squeeze out a little icing onto a paper towel or waxed paper to make sure it's flowing properly before proceeding to the next cookie.
Paint the Icing Gold
I have a detailed tutorial for painting royal icing with an edible gold luster dust suspension in my Painted Watercolor Cookies post.
Briefly, add some edible gold dust powder to the well of a food safe paint palette. I use a disposable transfer pipette to place a few drops of Everclear in the well and mix with a food safe paintbrush. You will need a very fine paintbrush for this.
I have tried other alcohols and have the best luck with Everclear due to the high alcohol percentage. It evaporates very quickly so it does not create pits in the icing.
To apply the gold to the royal icing, mix the suspension and allow the excess to run off the paintbrush. Then, carefully paint the gold on top of the lines of royal icing.
Allow the gold to dry before storing the cookies. The alcohol evaporates quickly.
Storage
You can leave the cookies out for many hours at room temperature for the icing to dry. To store, place in single layer in an airtight container. I do NOT recommend stacking the cookies. This can crush the design and cause the grease from the top cookie to disrupt the design on the bottom cookie.
If you must stack your cookies, I highly recommend placing pieces of aluminum foil between the layers. I have used waxed paper in the past and the grease still leaks through.
In my experience, these Shortbread Cookies get stale faster than Sugar Cookies. Plan to serve the shortbread within 1-2 days of making. For the sugar cookies, plan to serve anywhere from 1-5 days of making.
Technically you could freeze these cookies in a single layer in an airtight container. I always worry about freeze/thaw affecting the texture of the cookie, but the design should be ok as long as they are not stacked.
Gluten Free Option
Use your favorite gluten free sugar cookie or shortbread cookie recipe. I typically use a gluten free measure for measure flour, like Bob's Red Mill, in place of all purpose flour in cookie recipes. The resulting cookies are more crumbly than those made with all purpose flour, but they taste the same. Be extra careful taking them off of the cookie sheet.
To add the glaze, you'll want to carefully brush it on or pour it over the top rather than picking up the cookie to dunk in a bowl of glaze. The cookies will have the same delicious flavor but will be more crumbly than when made with AP flour. This is often the nature of gluten free cookies.
📖 Recipe
Diamond Gem Cookies
Equipment
- 2 ¼-inch wooden dowel rods
- 1 Rolling Pin
- 1 sharp paring knife
- disposable piping bags
- Plastic tip coupler optional
- small round piping tip, such as #2 optional
- plastic disposable transfer pipette
- food dedicated paint palette
- thin food grade paintbrush
Ingredients
- 1 batch cookie dough from your favorite shortbread cookie or cut out sugar cookie recipe (see note)
For the Icing Glaze:
- 2 cups powdered sugar
- ¼ cup milk
- ½ teaspoon clear vanilla extract or other clear extract like almond (rum or coconut)
- blue food coloring liquid
For Decorating:
- Easy Royal Icing (see note)
- white and blue sparkling sanding sugar
- edible gold luster dust
- Everclear, vodka or clear extract
Instructions
Bake the Cookies:
- Preheat oven to 350°F or temperature indicated in your chosen cookie dough recipe. Line 2 cookie sheets with parchment paper.
- Flour a cutting board or mat. Roll the dough out to ¼-inch thickness. It is helpful to use ¼-inch diameter wooden dowel rods on each side of the dough as guides for the rolling pin to ensure an even thickness.
- Cut the dough into diamond shapes of varying sizes with a sharp paring knife. It is basically a triangle with two corners (vertices) cut off.
- Place the cut dough shapes on parchment paper lined cookie sheets. Bake the cookies, one tray at a time, for 5-7 minutes, until baked through but not brown.
- Remove cookie sheet from the oven and allow cookies to cool for 1 to 2 minutes before removing them to a wire rack, then cool completely before glazing.
Glaze the Cookies:
- Place a wire rack over a parchment or waxed paper lined cookie sheet or work surface.
- Mix together the powdered sugar, milk, and extract. Using clear extract will keep the color of the icing white. Stir the icing together with a small spatula to avoid introducing bubbles. You can let the icing sit for a minute so bubbles rise and then pop them with the spatula. You can add more milk or powdered sugar to achieve a dippable consistency.2 cups powdered sugar, ¼ cup milk, ½ teaspoon clear vanilla extract or other clear extract like almond
- Drop blue food coloring liquid into the glaze and swirl with a toothpick. Be careful to just add a small amount of coloring. This is why I recommend using a liquid food coloring instead of a gel, as the gels tend to be very intense color.
- Dip the top surface of a cookie into the icing and place the cookies on the wire rack to allow excess glaze to drip off. This creates a marbled look. Use a toothpick to pop any bubbles on the surface of the glaze immediately after dipping.
- Repeat with all of the cookies. Allow the icing glaze to dry at room temperature until set, at least a few hours. If you want to allow them to dry overnight, place them in a single layer in an airtight container after the icing has partially set.
Add the Royal Icing Outline:
- Mix up outline consistency royal icing by adding about a half cup of the base icing to a small bowl. Add small amounts of warm water to the icing to thin it slightly so it is a pipeable consistency.
- Transfer the icing to a disposable piping bag fitted with a plastic tip coupler and a small round tip, such as a #2. Alternatively, cut off a very small opening in the tip of the piping bag.
- Locate the sanding sugars so you can use them immediately after piping the icing. Depending on the temperature and humidity of your kitchen, the icing can set quickly so you want to get the sugar on immediately.
- Start by piping an outline around the diamond shape.
- Pipe a line across the cookie to create the girdle of the diamond. The girdle separates the crown (top) of the diamond from the pavilion (bottom).
- Pipe a zigzag line across the crown to give the illusion of facets.
- Pipe two lines down across the pavilion that connect the girdle to the bottom point (culet), creating the illusion of facets on the pavilion.
- Immediately after piping, sprinkle white or blue sparkling sanding sugar onto the wet icing so it will stick. Shake off the excess sugar into a small bowl. This will allow you to reuse the sugar that does not stick to the cookie. Set the cookie aside on a baking rack to allow the icing to dry. Repeat the royal icing piping with the remaining cookies. Leave some cookies without sanding sugar to paint with edible gold after the icing has fully dried.
- Because you are working quickly and doing only 1 cookie at a time, you may need to cap off your piping tip between cookies or place the tip in a tall glass with a moist paper towel in the bottom. This should help prevent the icing from crusting over the tip. Make sure to check your tip for crusting each time before you begin piping the design. Sometimes I will just squeeze out a little icing onto a paper towel or waxed paper to make sure it's flowing properly before proceeding to the cookie.
- Allow the icing to dry, then shake or brush off any remaining excess sanding sugar.
Paint the Icing Gold:
- Add some edible gold dust powder to the well of a food safe paint palette.
- Use a disposable transfer pipette to place a few drops of Everclear in the well and mix with a food safe paintbrush. You will need a very fine paintbrush for this.
- Mix the suspension and allow the excess to run off the paintbrush. Carefully paint the gold on top of the lines of royal icing.
- Allow the gold to dry before storing the cookies. The alcohol evaporates quickly.
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