What’s the Difference Between Glass Slumping and Draping?

At one time or another, most of us have taken the opportunity to admire a handmade glass item with bold colors, flowing curves, or dramatic waves.

If you’re like me, you wondered how in the world it was made and if you could learn the technique yourself. 

Glass slumping and draping are two methods used to create shaped bowls, vases, platters, and more.

They are both relatively easy to learn and can quickly become addicting hobbies, but they are not the same thing.

What’s the difference between glass slumping and draping? Glass slumping is when a sheet of glass is heated to the point that the glass liquifies enough to settle into a concave mold. Glass draping is a similar process, but the glass is shaped over a convex mold. Draping results in more unpredictable designs.

Glass slumping and glass draping result in very different designs, so it’s important to understand the difference if you’re aiming for a specific look or have a certain function in mind for the finished piece.

Let’s examine how exactly they differ so you can decide which method you’d like to pursue.

Be warned, however, that you will likely want to try (and will fall in love with) both techniques.

Key Differences Between Glass Slumping and Draping

Both slumping and draping are techniques used to transform a sheet of glass into a totally new creation complete with lovely curves, depressions, or waves.

All kinds of bowls, plates, serving platters, catch-all trays, vases, and other decorative creations are possible once you are comfortable with the basics. 

Glass slumping and draping can be done with plain window glass (float glass), art glass, or even sheets of glass that you have fused yourself.

Before we proceed, let’s take a quick look at each method so we’re all on the same page.

Glass slumping is when a sheet of glass is balanced on the rim of a concave (curved inwards) mold.

Once placed in the kiln, the heat liquefies the glass to a point and gravity causes the melting glass to settle into the mold, taking the mold’s shape as it does so.

Slumping is usually used to make functional pieces such as bowls or deviled egg platters.

Glass Draping can be thought of as the opposite of slumping.

With draping, a sheet of glass is placed on a convex (curved outwards) mold. In the kiln, as with slumping, heat and gravity work to pull the glass down around the mold.

Draping is usually used to make fun items with a whimsical flair such as vases or catch-all trays. 

So, to be clear: 

With slumping, glass is shaped into a mold. With draping, glass is shaped over a mold.

While the two methods are similar in that they both use a mold and heat to form flat glass into exciting new shapes, there are several differences both in the process of making the piece and in the finished appearance.

When comparing a piece that has been slumped to one that was draped, one difference you’ll likely notice right away is that the slumped piece is shiny and glossy on the inside and slightly duller on the outside.

You’ll find that the draped item is exactly the opposite, with the outside being shinier than the inside.

Time

Slumping

When glass is slumped into a mold, the majority of the glass’ weight is being pulled down by gravity as the glass softens.

This is because, with most molds, only the corners and/or outer edges of the glass are supported by the mold.

So, the weight works to your advantage when slumping. You’ll notice that slumping begins soon after the kiln reaches the highest temperature in the firing.

That’s why the hold time at the highest set temperature is typically short.

Draping 

With glass draping, the edges of the sheet aren’t bearing the majority of the glass’ weight, so it can take much longer for the glass to begin to hang down the sides of the mold. 

Depending on the weight, type of glass, and mold used, it can take as long as an hour or even more at the highest temperature for the sides of the glass to drape over the form.

Edges

Slumping

With glass slumping, the edges of the glass tend to be quite uniform because they are supported to a certain degree by the mold, as demonstrated by the this mold.

When you place your piece in the kiln, you’ll have a fairly accurate idea of what the finished shape will look like. The edges should be reliably smooth, curved, and consistent.

The predictableness of the edges when slumping means that you can recreate your favorite items with a certain degree of accuracy, as long as you use the same type of glass and firing schedule. 

Draping

When glass is draped over a mold, like this one on Amazon, the edges are kind of left on their own to form curving, dramatic shapes. 

Of course, with more elaborate molds, the final edges are somewhat more predictable, but with simple molds, you will wind up with a unique creation every time.

Also, with draping, the form the edges will take largely depends on how long the piece is left at the highest temperature.

Other factors, such as how it is positioned on the mold, and the type and weight of the glass, will affect the edges as well. 

Basically, there are more variables that influence the shape of the edges when draping as compared to slumping.

Mold Material

Slumping

Generally, glass slumping is done in ceramic molds, although molds of rigid ceramic fiber board, fiber paper or blanket, kiln bricks, or mullite are sometimes used as well. 

These materials all expand and contract less than glass, so as the glass cools, it contracts away from the mold for easy removal.

Draping

Glass draping is usually done over a stainless steel mold because the steel expands and contracts more than glass, so it pulls away slightly from the glass resting on top of it. 

Ceramic molds or forms can be used as well, but cracking may occur more frequently due to the expanding/contracting rate of the material.

Can You Slump or Drape Without a Kiln?

If you had hopes of slumping or draping glass in your kitchen oven, I’m about to shatter your dreams.

An oven isn’t capable of producing the temperatures required for slumping or draping. 

However, some adventurous folks have had success slumping and draping items such as glass bottles over a fire to make spoon rests and other simple shapes. 

The temperature of a fire can be rather unpredictable, and hot glass heated or cooled improperly can explode, so use extreme caution. 

Let me be clear here. I am in no way encouraging this method; I’m only sharing the experience of others.

A standard campfire will typically reach about 900℉, while a large bonfire can exceed 2,000℉ easily, so plan on a slightly larger campfire to hit the ideal melting temperature of around 1,200℉. 

You can use a rock, a piece of ceramic tile or a standard mold as your form, but you’ll still need to apply a kiln wash prior to firing to prevent sticking. 

After the glass has slumped or draped to your liking, use long-handled, hot tongs to pull the mold and glass toward a cooler part of the fire.

Do not touch it again until the fire has gone out and the glass is completely cool.

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