Jake is with us.

I am looking for something for him to do.

We suggest he makes a gift for Hadley.

What can he make for her?

“What about soap?” says Maureen. “I once made some soap. It was fun.”

Jake looks doubtful.

“It’s chemistry. It’s not playdough”, Maureen said.

“What colour?”

“You decide. What do you think she would like?”

“Purple”, said Jake.

“I wonder how we do that?”

“Call Dr Brainstorm”, I said.

Dennis said we could use cochineal, madder or alkanet root for purple. But the soap mixture would need to be whitened with titanium oxide before adding the colorant. He said a hobbyist or craftsman might have alkanet root – what about Heather Atterbury?

He said he could bring round the titanium oxide. “I am also going to bring you pellets of lye, two pairs of goggles and rubber gloves.”

He had that stuff in his laboratory.

He was right about Heather. I went round and she gave us some of the powder in a resealable bag.

Maureen disappeared to look stuff up on the internet. I don’t think she wanted Dennis to take over the project completely.

She and Jake went to Tesco to buy the oils we did not already have.

By the time Dennis came she had laid out the equipment on a kitchen worktop: a bowl, a jug, a cutter, a shallow baking pan, scales and the various oils – olive oil, coconut oil, canola oil, sunflower oil, castor oil.

She asked Jake to mix them according to this recipe:

• 25% palm oil
• 25% coconut oil
• 25% olive oil
• 10% canola oil
• 10% sunflower oil
• 5% castor oil

Dennis said we should pour the lye pellets into the water outside in the open air because there would be a strong reaction and we should be sure to wear goggles and gloves and long-sleeved clothes.

Then he went away.

“We don’t need a chemistry lesson,” she said. I guess Maureen thought he was being finicky but she did as he suggested.

Then Maureen made Jake weigh and measure all the ingredients and take the temperature of the oils and the lye water so they were nearly equal before they were mixed.

Then she asked him to pour the lye water into the oil mix and told him to use the electric mixer in short bursts to help the soap form, first emptying in the titanium oxide powder.

Then as the soap began to set she told him when to add the alkanet root to get the purple colour.

Then when it was still quite soft, she helped him use a cutter to cut it into squares and wrapped it in an old towel and put it away in the larder to harden.

Dennis asked if he could come round and take a look. He peeked into the wrapped soap and said: “You must be a good student. It’s looking good. Nice colour too.”

“Was I a good recruit?”, said Jake.

I love the way kids like to try out words they have not used before.

“Obviously”, said Dennis.

Then Jake asked: “What actually happens when the lye mixture and the oils mix?”

Dennis said: “The vegetable oils are what are called triglycerides which combine fatty acids with glycerol. The lye, which is sodium hydroxide, combines with the fatty acids and releases the glycerol, I can draw it out for you if you like….”

And he took a sheet of paper and a pencil and did so, while Maureen and I cleared the things away.

I meant to ask Jake why he chose purple but I forgot.