Blood, Iron and Light door (study door puzzle)

Where the puzzle is

The door is in Iván's apartment on the 3rd floor, the room you start the game in. It is the study door with a red symbol on it; Julia can't open it at first.

The clue is in the Old Book lying on the apartment floor: the red seal (Lapis Fictus) dissolves with Auritsatio, made from the acids of Tartarus, tamed by iron and blessed by sunlight. The Developing Chemical is the acid (its description mentions tartaric acid), and the iron is your own blood.

Not sure you’re in the right place? Search for your room in Quick find tool.

What you need

• Wrench: Iván's bathroom, behind the shower curtain
• Developing Chemical: in the kitchen fridge
• Glass: Iván's bedroom, next to the lamp
• Old Book: on the apartment floor (it has the recipe; you can solve the door without reading it)

Exact spots for each one are on Items and collectibles.

Step by step

1. Collect the Wrench, the Developing Chemical and the Glass

   All three are inside the apartment: the Wrench is behind the shower curtain in the bathroom, the Developing Chemical is in the kitchen fridge, and the Glass stands beside the bedroom lamp.

2. Use the Glass at the broken bathroom mirror

   Stand at the cracked mirror and use the Glass. Julia cuts herself and the item becomes Glass with Blood.

3. Combine Glass with Blood with the Developing Chemical

   Open the inventory and combine the two. You now hold Glass with Chemical and Blood.

4. Let sunlight into the bedroom

   In Iván's bedroom, open the blinds, then hit the boarded-up window with the Wrench until the boards break and sunlight comes in.

   

5. Bless the mixture in the sunlight

   Stand next to the sunlit window and use Glass with Chemical and Blood. It turns into Auritsatio.

6. Use the Auritsatio on the study door

   Walk to the door with the red symbol and use the Auritsatio in front of it. The seal dissolves and the study opens.

   

If it doesn’t work

Using the mixture does nothing.

You have to stand right by the bedroom window after the boards are broken. If the window is still boarded, keep hitting it with the Wrench.

I can't find the Glass.

It is on the small table next to the lamp in Iván's bedroom, not in the kitchen.

The mirror won't let me use the Glass.

Use the plain Glass, not the Developing Chemical. The blood step comes first; you combine with the chemical afterwards.

Sources

1. Tenebris Somnia - All Puzzles & Solutions Guide by iampanax Timestamps used: 0:00–2:13
2. Tenebris Somnia Full Game Walkthrough - All 4 Endings [No Commentary] by iampanax Timestamps used: 1:56
3. Tenebris Somnia Full Puzzles Walkthrough (Gamer Social Club, used to confirm the step order) by Mark Pell