The easiest way to create a Soft Rubber Stone of Quality 50 is by leveling up the recipe’s Quality loop. You can do it by synthesizing high Red Quality Supplements and adding them to the Soft Rubber Stone recipe.

The Soft Rubber Stone is a mandatory item to complete Chapter 3 – Everyone’s Changing, part 3.

Make sure to clear the following requirements to synthesize the recipe:

1. Raise your Alchemy Level: The Soft Rubber Stone requires at least Alchemy Level 7. Alchemy Level 10 allows you to add one extra ingredient to the recipe, but it won’t be necessary this time.
2. Obtain the necessary ingredients: You will require at least one Fruit type ingredient and one Puniball.
3. Synthesize high Quality Red Supplements: Adding Red Supplements to the recipe’s Quality loop is the easiest way to clear this quest. Make sure you have at least two high Quality Red Supplements.

Gathering the Ingredients

The Puniball is a common drop from defeating Punis. You can use any Fruit type ingredient for the other loop.

The most important part will be synthesizing the high Quality Red Supplements. Start by gathering Health flowers outside Ryza’s Atelier.

You can also collect Clean Water from the pond.

After collecting the ingredients, head back inside the Atelier to start synthesizing the Red Supplements. Use the Auto-Add function and select “High Quality”.

You should now have the necessary ingredients to increase the Soft Rubber Stone’s Quality.

Synthesizing the Quality 50 Soft Rubber Stone

Next, scroll down the recipe list and select the Soft Rubber Stone. 

The Quality loop is located on the right side of the recipe. It requires at least Fire Element 3 to level up, which is why you specifically need Red Supplements.

Start by inserting the Fruit ingredient into the Effect 1 loop.

Follow it up by inserting the Puniball into the Effect 3 loop. Do not use the other loops, as you will need to save ingredients for the Quality loop.

After inserting the Puniball, you will unlock the Quality loop. Insert the first high Quality Red Supplement.

Add a second high Quality Red Supplement. It will level up the Quality loop, adding 15 Quality to the Soft Rubber Stone.

You have met the Quality 50 requirement while only using four ingredients.

Synthesize the recipe to obtain the Soft Rubber Stone.

Take the Soft Rubber Stone to Lubart Valentz and you will clear the quest.