Here are a few things to consider when picking a container for gelatin art:
1. Shape
2. Size / Depth
3. Thickness
4. Material / Transparency
Shape
The shape of the container is the most important feature when it comes to selecting containers for gelatin art. Not only will the container act as a mold for the dessert, but it will also affect the way drawn flowers look within the dessert. For example, a perfectly round container will act as a magnifying glass and make your flowers appear a lot bigger that they are. This could work to your advantage as you will be able to fill the entire dessert with a few small flowers, but it could also make your dessert seem over-crowded if you are not careful.
A half-sphere shape seems to be the best choice for small individual flowers as there are no sharp edges to cause the dessert contents to look distorted.
Containers with a perfectly round top are a favorite choice as they leave a very smooth looking dessert, but it can be tricky to get them to stand straight while you draw.
You can put round containers in a cup or a small bowl to help it stay in place. A small cookie cutter might come in handy too, but be careful not to scratch the container surface with it.
If you are making a larger batch, you can use a muffin baking pan to keep the round containers standing straight while the gelatin is setting in the fridge.
A half-sphere container with a flat top is the next best choice. It will give you a nice looking dessert and it will easily stay in place and allow you to work on your flowers without worrying about tipping it over.
The trick with the flat top is to pick a container that only has a tiny flat area. A small container with a large flat top will completely distort the flowers you draw into it.
Sharp edge shapes and semi-sharp edge shapes work well for larger deserts. The sharp edged gelatin dessert looks crisp and elegant, but it can be tricky to get it out of the container.
Even though the dessert edges get melted enough to be released from the container, sharp edges stick snugly to the container and don't allow any air to enter. This creates vacuum at the top of the container and the dessert cannot fall out when turned upside down.
If this happens, pull the dessert edge gently or insert a straw or a toothpick to allow the air to enter the top of the container. When the dessert is out, check if the air has caused some melted gelatin or mousse to rise along the edges and make the dessert look messy. If that happens, use a bit of water to wash the unwanted smudges down.
Uneven shapes, such as custom jelly shapes and molds usually don't produce good results. The curves of the mold make the flowers within gelatin hard to see and recognize.
Size / Depth
Decide what kind of a flower you wish to draw before selecting the container.
Even the biggest containers will distort the look of the drawn flowers around their edges.
Make sure your flowers can fit comfortably without reaching the container edge. Keeping the flowers in the middle and leaves closer to the edge helps alleviate the distortion problems somewhat.
Another thing to watch out for is the container depth. Container should always be filled as high as possible to make it easier to draw in it. If a container is only half full, it will be hard to draw flowers in it because of the awkward angle the container wall dictates.
Always fill the container with as much gelatin as it can safely take to avoid being restricted by the container edge.
For this reason, if you will be drawing the flowers directly in the large container, you might want to chose a flat container.
If you are using a large spherical container, create large, bold flowers in it, otherwise you will end up with a lot of empty gelatin on top and small foggy flowers on the bottom.
Another option for large containers is to fill them up with small gelatin desserts and melt them together into one large dessert.
You can find the instructions for making large gelatin desserts in our instructions section.
Thickness
The thickness of the container is important when you are handling gelatin that has not completely set and, also, when you are taking the dessert out of the container.
Gelatin art containers don't have to be thick, gelatin will hold it's shape once it has thickened up. The problem, however, is handling gelatin in a thin container while it is in liquid form and hasn't completely set yet.
The best way to deal with thin containers is to use 2 or 3 containers together.
Place several containers of the same shape together and use them as one container until the gelatin has set. 
You can also place the thin container on a serving platter or a plate before you fill it with gelatin. That way you can lift it and place it in the fridge easily.
Thickness also plays a very important role when the dessert is being taken out of the container. The thicker the container wall, the longer it will take for the gelatin to melt and release itself from the container. This is especially problematic if you are using a container whose walls are not of consistent thickness. For example, glass bowls and casserole pans might have an enforced bottom to prevent them from breaking easily. If you place such a container into warm water, the dessert edges will melt a lot faster than the top and you might lose too much of your edges before the dessert can come out or you might be fooled by the loosened edges and turn your dessert too early causing it to tear with the top still stuck onto the container.
The best way to deal with uneven containers is to insert then into water gradually. Let the bottom touch the warm water for a while before submerging it completely.
Experiment until you find the perfect timing for your containers and the water temperature you use.
Material / Transparency
Glass containers are a good choice for gelatin art as they offer great transparency and a firm mold for gelatin. Most of us already have a few glass bowls or casserole dishes in our kitchen which makes them a great, zero-cost choice if you are just getting started with gelatin art and don't want to spend too much money on supplies. They are also very handy for large gelatin desserts as they hold their shape and don't get deformed under the heavy weight of gelatin. They are also much more scratch resistant than plastic containers.
The down-side of glass containers is that they are generally a lot heavier than plastic containers. They also take more time to heat up and release the dessert.
Plastic containers offer a great alternative to glass. They are not as sturdy but offer sufficient support and transparency to create beautiful desserts.
Unlike glass containers, disposable plastic containers can be given away with the dessert, allowing the dessert to last longer and maintain it's perfect shape within the container.
This also passes along the responsibility of taking the dessert out of the container (unharmed) to the recipient of the gift. This is a great advantage when you are creating dozens of desserts for bake sales or other events.
Some plastic containers scratch easily. You might notice small dents and scratches on a container after you have drawn your design into them.
If you are working with delicate containers, designate one as the scratch guard and place other containers into it while you are working. The top container will absorb all the damage and the inner one will remain smooth and perfect.
Also, avoid using harsh sponges and brushes when you are washing your containers.
Metal containers are not used often as they are not transparent and don't allow you to see what your dessert looks like while you are working, however, many of us have funky looking baking pans that would be perfect for gelatin desserts.
You can draw your flowers directly into a metal container filled with gelatin and hope for the best, but it might be a safer bet to use the metal pan to assemble several smaller desserts, that you already see and like, into one larger container.
When it comes to taking gelatin out of it's container, metal is the easiest choice. It heats up fast and releases the gelatin within a few seconds. Since very little gelatin melts around the edges, the dessert maintains a crisp and sharp shape.
Find more gelatin art related topics on our Instructions page.