Clay-Fired Bricks // Cosmium Kiln — ruling 1

The back faces of some cards with craft refer to cards "used to craft" it. This refers to the cards exiled as part of the cost of the craft ability of the front face. Those cards are considered to be "used to craft" that permanent as long as they remain exiled and the permanent remains on the battlefield, even if the permanent's controller changes or some of its characteristics change (because of a copy effect, for example.)

Clay-Fired Bricks // Cosmium Kiln — ruling 2

If the materials required include multiple objects, you may exile some of them from among permanents you control and the rest from among cards in your graveyard. You don't have to choose all permanents or all cards from your graveyard.

Clay-Fired Bricks // Cosmium Kiln — ruling 3

You may exile tokens you control as part of the materials required. However, because they aren't cards and won't stay in exile, any abilities that refer to what you "used to craft" the back faces won't refer to anything.

Clay-Fired Bricks // Cosmium Kiln — ruling 4

If a card that isn't a transforming double-faced card becomes a copy of a card with craft, it'll stay in exile if you activate the craft ability. It won't return to the battlefield.

Clay-Fired Bricks // Cosmium Kiln : règles, fonctionnement et interactions (MTG)

Clay-Fired Bricks // Cosmium Kiln is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

When this artifact enters, search your library for a basic Plains card, reveal it, put it into your hand, then shuffle. You gain 2 life. Craft with artifact (, Exile this artifact, Exile another artifact you control or an artifact card from your graveyard: Return this card transformed under its owner's control. Craft only as a sorcery.) When this artifact enters, create two 1/1 colorless Gnome artifact creature tokens. Creatures you control get +1/+1.

How it works : Clay-Fired Bricks // Cosmium Kiln

Original English text — Wizards of the Coast / Scryfall

#1November 10, 2023· Wizards of the Coast
The back faces of some cards with craft refer to cards "used to craft" it. This refers to the cards exiled as part of the cost of the craft ability of the front face. Those cards are considered to be "used to craft" that permanent as long as they remain exiled and the permanent remains on the battlefield, even if the permanent's controller changes or some of its characteristics change (because of a copy effect, for example.)
No other card is named in this ruling.
#2November 10, 2023· Wizards of the Coast
If the materials required include multiple objects, you may exile some of them from among permanents you control and the rest from among cards in your graveyard. You don't have to choose all permanents or all cards from your graveyard.
No other card is named in this ruling.
#3November 10, 2023· Wizards of the Coast
You may exile tokens you control as part of the materials required. However, because they aren't cards and won't stay in exile, any abilities that refer to what you "used to craft" the back faces won't refer to anything.
No other card is named in this ruling.
#4November 10, 2023· Wizards of the Coast
If a card that isn't a transforming double-faced card becomes a copy of a card with craft, it'll stay in exile if you activate the craft ability. It won't return to the battlefield.
No other card is named in this ruling.